UNIVERSITY  OF  CALIFORNIA 

ANDREW 

SMITH 

HALLIDIC: 


AMERICAN 
METER    PRACTICE 


BY 


LYMAN    C.    REED 


NEW  YORK 

McGRAW  PUBLISHING  COMPANY 

1 1 4  Liberty  Street 

1903 


COPYRIGHTED,   1903 

BY  THE 

McGRAW  PUBLISHING  COMPANY 
NEW  YORK 


\ 


PREFACE 


THE  subject  of  metering  the  output  of  central  stations 
has  been  to  me  one  of  the  most  interesting  of  the 
many  problems  arising  in  the  development  of  the  supply 
of  current  for  various  commercial  needs;  There  are  many 
minor  details  omitted  in  the  work,  which  would  doubtless 
prove  of  interest  to  the  practical  worker  in  meters,  but, 
however  poorly  set  forth,  the  effort  is  made  to  outline  the 
underlying  principles  of  operation  and  practice  and  leave 
the  minor  details  to  be  worked  out  to  suit  local  conditions. 

In  describing  only  a  few  meters  my  object  is  to  select  one 
each  of  well  known  and  representative  types  and  not 
to  weary  the  reader  by  reciting  the  same  characteristics 
held  by  a  number  of  meters  of  the  same  type. 

Any  intention  of  slighting  in  any  way  many  excellent 
meters,  herein  mentioned  but  not  described,  is  entirely 
foreign  to  the  purpose  of  this  work.  The  meters  selected 
have  each  some  distinguishing  feature  which  makes  them 
representative  of  as  many  respective  classes. 

To  the  consumer  of  power  who  is  not  a  technical  man, 
Chapter  XIII,  on  How  to  Read  Meters,  will  probably  be 
of  most  interest  since  it  will  enable  him  to  figure  out  and 
check  up  his  meter  bills.  This  knowledge  should  bring 
about  the  very  friendliest  relations  between  the  supplier 
and  consumer  of  electricity. 

LYMAN  C.  REED. 

3 


141415 


CONTENTS 


Chapter         I — Measurement   of    Power  in    Direct 

Current  Circuits 7 

Chapter  II — Measurement  of  Power  in  Alternat- 
ing Current  Circuits 17 

Chapter  III — Meter  Selection  ;  Requisites  of  a 
Good  Meter ;  Commercial  Consider- 
ations   34 

Chapter      IV — Torque  and  Friction 46 

Chapter        V — The  Edison  Chemical  Meter 59 

Chapter      VI — The  Thomson  Recording  Wattmeter  67 

Chapter    VII — The  Duncan  Recording  Wattmeter 

for  Alternating  Current 82 

Chapter  VIII— The  Duncan  Wattmeter  for  Direct 

Current 91 

Chapter      IX — The  Stanley  Recording  Wattmeter .        105 

Chapter       X— The  Guttman  Wattmeter 113 

Chapter      XI — The  Westinghouse  Induction  Meter .        119 

Chapter  XII — General  Management  of  the  Meter 
Department ;  Records  ;  Testing  ; 
General  Policy 124 

Chapter  XIII — Reading  Meters 159 

Chapter    XIV — Value  of  Losses  in  Meters  Relative 

to  Income 163 

Chapter     XV — Differential  Rating 171 

Chapter  XVI— Elements  of  Photometry 178 

5 


AMERICAN   METER  PRACTICE. 


CHAPTER  I. 
Measurement  of  Power  in  Direct  Current  Circuits. 

Electrical  measurements  in  the  laboratory  have  been 
carried  on  for  many  years  with  great  accuracy.  The  con- 
ditions are  carefully  studied  when  a  determination  of  some 
quantity  is  sought,  and  the  errors  which  effect  the  accur- 
acy of  the  measurement  eliminated.  The  study  of  the 
phenomena  of  electricity  is  rightly  called  an  exact  science, 
but  the  perfecting  of  an  accurate  commercial  meter  has 
been  a  slow  and  tedious  process.  At  first  the  principles  of 
correct  design  were  not  embodied  in  the  meters  put  on  the 
market,  and  no  matter  how  perfect  they  were  made  me- 
chanically a  correct  registration  of  the  power  consumed 
could  not  be  obtained.  But,  as  a  rule,  the  mechanical 
features  were  more  defective  than  the  theoretical  ones,  and 
the  combination  of  these  defective  elements  has  given  the 
meter  of  commerce  an  unenviable  reputation. 

Such  great  inventors  as  Edison,  Thomson,  Shallenberger 
and  Duncan  have  spent  much  time  in  trying  to  get  to- 
gether various  elements  in  suitable  combination  to  meet 
the  requirements  and  accurately  measure  the  current  or 
the  power  in  the  many  various  applications  and  uses  to 
which  electricity  is  put.  Edison  gave  us  the  chemical 
ampere  hour  meter,  which  has  done  yeoman  service  in  the 


8  AMERICAN  METER  PRACTICE. 

metering  of  direct  currents;  and  Thomson  gave  us  his 
recording  wattmeter,  which  has  gradually  been  developed 
into  an  excellent  meter,  and  which  can  be  used  for  both 
direct  and  alternating  current.  Shallenberger  and  Dun- 
can produced  at  first  ampere  hour  meters  for  alternating 
current,  but  in  later  years  wattmeters,  also,  for  alternating 
current.  There  is  a  large  number  of  other  meters,  but 
these  four  are  the  pioneers  in  the  meter  field.  In  each 
meter  different  principles  are  involved,  which  meet  more 
or  less  successfully  the  requisite  of  a  good  commercial 
meter.  Heat  and  cold,  moisture,  dust,  insects  and  vibra- 
tion are  some  of  the  physical  obstacles  to  be  met  and  over- 
come by  the  successful  meter;  and  short  circuits,  over- 
loads, light  loads  and  no  loads  are  some  of  the  electrical 
conditions  under  which  it  must  operate.  The  wearing 
qualities  of  all  of  the  elements  of  the  meter  must  be  taken 
into  consideration.  As  in  the  one-horse  chaise,  each  part 
of  the  meter  should  be  as  strong  as  any  other  part.  The 
ability  to  withstand  the  test  of  time;  the  property  of 
being  the  same  meter  at  the  end  of  one  year's  use,  is  the 
real  test  of  the  value  of  an  instrument.  The  problem, 
then,  becomes  one  of  combining  certain  elements  in  such 
relation  to  each  other  as  to  form  a  perfect  measuring 
device,  and  the  maintaining  of  this  same  relation  in  the 
face  of  the  various  conditions  which  are  partially  enumer- 
ated above.  However  clearly  these  principles  were 
recognized  twenty  years  ago,  the  state  of  the  art  was  such 
that  only  very  imperfect  devices  were  produced  as  meters. 
It  has  been  only  within  the  last  few  years  that  com- 
mercial meters  have  been  brought  to  a  reasonable  state  of 
efficiency.  The  vast  interests  involved  have  quickened 
the  managements  of  central  stations  to  the  importance  of 
having  better  meters  and  meter  service,  and  the  field  of  in- 


MEASUREMENT  OF  POWER.  9 

vention  is  so  attractive  along  these  lines  that  we  see  each 
year  a  gradual  improvement  in  the  design  and  performance 
of  the  meters  placed  on  the  market. 

The  measurement  of  any  form  of  transmitted  energy  is 
always  attended  by  a  diminution  of  the  energy  trans- 
mitted equal  to  the  amount  consumed  in  the  measuring 
device. 

Hence  all  instruments  that  measure  transmitted  energy 
are  shunt  instruments,  the  power  shunted  or  diverted  from 
the  transmission  being  usually  a  very  small  fraction  of  the 
total  power.  We  may  class  all  such  devices  as  shunt 
dynamometers  to  distinguish  them  from  absorption 
dynamometers,  which  usually  translate  the  energy  to  be 
measured  into  heat  or  mechanical  work  and  destroy  its 
original  properties. 

The  measurement  of  electrical  energy  which  is  trans- 
mitted is  accomplished  by  means  of  shunt  dynamometers. 
Its  translation  into  useful  commercial  forms  is  accom- 
plished by  absorption  dynamometers  of  various  cjasses, 
such  as  motors  and  incandescent  lamps. 

For  the  sake  of  analysis  the  flow  of  electrical  energy  is 
usually  considered  by  treating  its  two  components,  quan- 
tity and  intensity,  as  individual  entities,  and  instruments 
are  constructed  which  will  measure  each  separately  as 
well  as  the  product  of  the  two. 

In  commercial  circuits  the  voltage  or  intensity  usually 
remains  constant,  in  which  case  a  measurement  of  the 
power  flowing  in  a  circuit  may  be  obtained  by  the  record- 
ing of  the  variable  quantity  of  current  in  amperes  and 
multiplying  by  the  known  voltage.  If  the  amperes  remain 
constant,  and  the  voltage  vary,  a  record  can  be  obtained 
of  the  power  flowing  by  recording  the  variable  voltage  and 
multiplying  by  the  known  amperes  of  the  circuit.  If  both 


10  AMERICAN  METER  PRACTICE. 

the  voltage  and  the  amperage  of  the  circuit  be  variable 
their  product  gives  the  power  flowing,  which,  for  conveni- 
ence, is  usually  indicated  by  one  instrument  called  a  watt- 
meter. 

In  the  first  class  of  instruments,  the  ammeter  class,  the 
loss  in  energy  due  to  the  insertion  of  the  instrument  in  the 
circuit  is  directly  proportional  to  the  current  flowing. 

The  voltmeter,  if  on  a  constant  potential  circuit,  has  a 
constant  energy  consumption  The  wattmeter  has  a  con- 
stant energy  consumption  in  its  potential  circuit  plus  a 
variable  energy  loss  in  the  series  circuit  proportional  to  the 
current  flowing. 

From  the  foregoing  the  deduction  follows  that  on  con- 
stant potential  circuits  of  known  intensity  the  measure- 
ment of  the  energy  passing  is  the  most  economically  carried 
out  by  an  ammeter,  on  circuits  of  constant  and  known 
amperage  with  variable  voltage  by  a  voltmeter,  and 
where  both  current  and  voltage  are  variable  by  a  watt- 
meter. 

These  general  statements  hold  true  for  the  measurement 
of  the  power  in  a  direct  current  circuit,  or  a  non-inductive 
alternating  circuit,  but  must  be  modified  for  inductive 
alternating  circuits  containing  reactance  and  capacity, 
the  effects  of  which  will  be  brought  out  in  Chapter  II. 

It  is  assumed  that  the  reader  is  familiar  with  the  well- 
known  forms  of  indicating  ammeters,  voltmeters  and 
wattmeters  on  the  market,  the  descriptions  of  which  are, 
therefore,  omitted. 

Many  of  these  instruments  record  the  passing  power  of  a 
circuit  with  extreme  accuracy,  but  being  simply  indicators 
of  the  instantaneous  values  of  the  power  they  do  not  give  a 
summation  of  this  power  during  the  elapsed  time.* 

*See  Flather's  Dynamometers  and  Measurement  of  Power. 


MEASUREMENT  OF  POWER.  11 

In  order  that  an  instrument  may  bring  in  the  element  of 
time  in  the  measurement  of  power,  it  must  constantly 
move  some  object,  for  one  unit  of  energy  passing,  through 
unit  distance  in  unit  time;  and  this  movement  must  be 
permanently  recorded  by  means  of  a  dial  train,  or  some  sim- 
ilar summation  device.  Then,  when  n  units  of  energy  are 
passing,  the  recording  object  will  be  moved  through  n 
units  of  distance  in  unit  of  time.  The  application  of  this 
principle  to  commercial  recording  meters  has  resulted  in 


FIG.  1. 

a  great  number  of  types,  the  most  prominent  of  which 
are  described  in  succeeding  chapters. 

The  various  classes  of  electrical  energy  to  be  measured 
commercially  resolve  themselves  into: 

Direct  current  as  distributed  by  two  or  three-wire 
systems. 

Alternating  current,  single  and  polyphase  systems. 

Direct  current  distributed  by  means  of  a  five-wire 
system  is  also  used  to  some  extent,  but,  as  the  principles 
involved  in  its  measurement  are  identical  with  those  of  the 
two  and  three- wire  systems,  the  five- wire  system  will  not 
be  considered  separately. 

Two-wire  direct  current  systems  are  usually  confined  to 
500  volt,  and  arc  circuits.  The  three- wire  system  is  the 
well  known  Edison  system,  the  local  distribution  of  which 
may  be  either  two  or  three- wire. 

The  amperes  flowing  in  the  simple  two-wire  circuit  with 
load  at  C,  Fig.  i,  are  the  same  in  every  part  of  the  circuit. 


12  AMERICAN  METER  PRACTICE. 

An  ammeter  placed  at  A  reads  the  same  as  if  placed  at  B, 
but  the  energy  in  the  circuit  varies  as  the  distance  from  D, 
becoming  less  as  C  is  approached,  and  is  directly  propor- 
tional in  a  circuit  of  uniform  resistance  to  the  distance  from 
D.  Hence  the  mean  power  in  the  circuit  would  be  found  at 
some  point  between  D  and  C. 

It  is  customary  in  an  ordinary  two-wire  service  to  meter 
the  energy  passing  at  A,  and,  if  the  fall  of  potential,  or  loss 
of  energy,  between  A  and  C  be  small,  the  error  is  not  great, 
the  allowable  loss  usually  not  exceeding  two  per  cent., 
hence  one  per  cent,  less  energy  than  that  recorded  at  A 
would  represent  the  mean  energy  passing  in  the  given 
circuit. 

As  the  meter  in  commercial  practice  is  placed  at  the  en- 
trance of  the  service  into  a  building,  the  consumer  usually 
pays  for  about  one  per  cent,  more  energy  than  he  actually 
receives  at  his  translating  devices. 

Should  the  meter  be  a  recording  ammeter,  one  leg  of  the 
circuit  only  passes  through  the  instrument ;  if  a  wattmeter 
be  used  the  other  leg  of  the  circuit  must  be  brought  into  the 
meter  to  enable  the  potential  coils  of  the  instrument  to  be 
energized. 

In  a  recording  wattmeter,  the  product  of  the  magnetiza- 
tion set  up  by  the  series  and  shunt  field  coils  must  exert  a 
resultant  torque  on  some  movable  member  of  the  meter 
which  will  cause  it  to  move  in  a  manner  to  record  n  units  of 
energy  in  n  units  of  time. 

The  movable  members  of  a  recording  instrument  have,  un- 
fortunately, an  appreciable  amount  of  friction  which  intro- 
duces an  inertia  factor  operating  as  a  counter  torque  to  the 
product  of  the  energy  torque  by  a  function  of  time.  This 
friction  of  the  moving  parts  is  small,  and,  at  full  load  of  the 
meter,  the  ratio  between  the  counter  torque,  due  to  friction, 


MEASUREMENT  OF  POWER.  13 

and  the  energy  torque  is  negligible.  As  the  load  decreases, 
the  ratio  between  the  counter  frictional  torque  and  the 
energy  torque  approaches  unity;  in  other  words,  there  is  a 
certain  point  in  every  recording  instrument  where  the 
energy  torque  and  frictional  torque  are  equal.  When  this 
point  is  reached  the  instrument  remains  at  rest. 

The  counter  frictional  torque  varies  in  different  instru- 
ments of  the  same  and  different  makes  from  a  fraction 
of  one  per  cent,  to  three  or  four  per  cent,  of  full  load 
energy  torque,  the  large  losses  often  being  due  to  causes 
arising  in  service. 

For  this  reason,  it  is  customary  in  commercial  recording 
instruments  to  compensate  for  this  friction  by  introducing 


>b 


FIG.  2. 

an  additional  torque  which  is  a  definite  fraction  of  full  load 
value,  and  which  compensates  through  all  ranges  of  load 
for  the  initial  friction  of  the  meter. 

Theoretically  this  is  a  very  pretty  way  of  accomplishing 
the  result,  but  exactions  of  service  introduce  frictions 
which  this  compensation  does  not  entirely  eliminate. 

The  power  passing  in  a  three-wire  circuit  is  usually 
measured  by  metering  the  two  outside  legs,  although  equally 
good  results  can  be  obtained  by  metering  one  outside  leg 
and  the  neutral  conductor. 

In  the  three-wire  circuit,  Fig.  2,  let  A,  B,  D,  C  be  the 


14  AMERICAN  METER  PRACTICE. 

outside    legs,    E    the    neutral    conductor,    and    b    and    c 
translating  devices. 

When  the  currents  in  A  B  and  D  C  are  equal  no  current 
flows  in  E ;  when  they  are  unequal  E  carries  the  difference 
positive  or  negative.  The  energy  flowing  on  each  side  of 
the  system  can  be  measured  by  two  two-wire  meters,  or  one 
three-wire  meter.  In  either  case,  the  series  coils  carry  the 
varying  amperes  of  each  side  of  the  system,  while  the  shunt 
field  coils  are  energized  proportionately  to  the  voltage  of  the 
system. 

If  two  two-wire  meters  be  used,  the  same  connections 
are  made  as  in  a  two-wire  system.  If  a  three-wire  meter 
be  used,  the  two  series  fields  are  superposed  to  form  a  re- 
sultant field  proportional  to  the  current  flowing  in  both 
sides  of  the  system.  The  torque  due  to  this  resultant  field 
and  the  field  set  up  by  the  potential  circuit  operates  the 
meter  in  such  a  manner  as  to  record  the  total  energy 
passing  in  the  three-wire  circuit. 

A  form  of  meter  which  is  not  manufactured  commerci- 
ally, so  far  as  the  author  is  aware,  can  be  constructed  to 
measure  the  total  energy  flowing  in  a  three-wire  circuit  by 
placing  one  series  coil  of  an  ordinary  three-wire  meter  in 
one  outside  leg  of  the  circuit  and  a  coil  of  half  the  number 
of  turns  in  series  with  the  neutral.  The  power  registered  is 
multiplied  by  two. 

To  illustrate,  suppose  A  B,  Fig  2,  to  carry  50  amperes, 
positive,  and  D  C  2$  amperes,  negative,  then  the  neutral 
wire,  E,  carries  25  amperes,  negative.  As  the  neutral  field 
coil  has  half  the  number  of  turns,  the  sum  of  the  magnetiza- 
tions of  the  series  fields  is  equal  in  effect  to  a  positive  cur- 
rent of  37.5  amperes.  Twice  this  amount  is  75  amperes,  or 
the  same  as  the  series  fields  of  the  ordinary  three-wire  meter 
would  carry  in  the  example  given. 


MEASUREMENT  OF  POWER.  15 

The  PR  losses  in  the  fields  of  a  meter  at  full  load  reach 
an  appreciable  amount,  but  at  light  loads  are  not  of  much 
consequence,  hence,  in  the  form  of  meter  just  given,  on  a 
properly  balanced  three-wire  service  the  PR  losses  would 
be  halved  as  the  neutral  would  carry  no  current.  On 
unbalanced  loads  the  loss  in  this  form  of  meter  would  be 
reduced  by  some  quantity  varying  between  the  limits  of 
J  and  —  J,  so  that  an  average  saving  in  PR  losses  in  the 
field  coils  for  any  meter  would  be  12 \  percent.  In  reality 
this  would  be  much  larger,  as  any  serious  unbalancing 
would  scarcely  take  place  except  at  light  loads,  when  the 
PR  losses  are  negligible. 

The  shunt  field  coil,  where  a  single  meter  is  employed, 
can' be  fed  from  across  the  outside  or  between  the  neutral 
and  one  outside.  In  either  arrangement,  unless  the  volt- 
age be  equal  on  both  sides  of  the  system,  an  error  is  intro- 
duced into  the  record  proportional  to  the  difference  of 
voltage  existing.  To  obtain  a  true  record,  if  the  voltage  be 
unequal,  it  is  necessary  to  employ  two  two-wire  meters  or  a 
three-wire  meter  having  two  armatures  fed  respectively 
from  each  side  of  the  system. 

The  latter  arrangement  amounts  to  the  combining  of  two 
meters  under  one  cover,  resulting  in  a  clumsy  and  expensive 
device.  In  commercial  practice  the  voltage  on  one  side  of 
a  three- wire  distributing  system  is  usually  maintained 
about  equal  to  that  on  the  other;  the  errors  resulting 
from  inequalities  of  the  sides  supposedly  balance,  so  that 
it  is  the  usual  practice  to  meter  with  a  three-wire  meter 
with  the  shunt  field  coils  fed  between  the  two  outsides 
or  between  one  outside  and  neutral. 

In  meters  of  the  class  described,  the  torque  urging  the 
rotary  part  at  any  given  moment  is  proportional  to  the 
energy  of  the  current  at  that  moment,  while,  to  record 


16  AMERICAN  METER  PRACTICE. 

correctly,  the  speed  must  be  proportional  to  the  energy, 
and,  consequently,  to  the  torque.  This  result  is  secured  by 
providing  a  breaking  device  in  which  the  resistance  offered 
to  rotation  is  proportional  to  the  speed. 

This  brake  may  be  of  various  constructions,  but  the 
usual  form  is  that  of  a  conducting  non-magnetic  metallic 
disk  revolving  between  the  poles  of  a  permanent  magnet. 
The  eddy  currents  generated  in  the  disk,  by  their  reaction 
on  the  permanent  magnetic  field,  exert  a  resistance  to 
movement  which  varies  in  amount  proportionately  to  the 
speed  of  the  torque  exerted  by  the  moving  member  to 
which  the  disk  is  fixed.  Hence,  the  power  necessary  to  gen- 
erate the  eddy  currents  becomes  proportional  to  the  torque 
exerted  on  the  moving  member  or  the  watts  passing  in  the 
circuit.  Other  forms  of  brakes  are  employed,  such  as  fans 
and  liquid  brakes,  but  they  have  given  place  in  the  latest 
types  of  meters  to  the  now  universal  magnetic  brake. 


CHAPTER  II. 
Measurement   of  Power  in  Alternating  Current  Circuits. 

In  passing  to  the  measurement  of  alternating  currents, 
simple  two  and  three-wire  non-inductive  single-phase 
circuits  will  be  first  considered. 

The  power  flowing  in  a  non-inductive  two-wire  circuit  is 
at  any  instant  the  product  of  the  instantaneous  values  of 
the  current  and  voltage.  To  get  the  mean  power  the  in- 


FIG.  3. 

stantaneous  values  must  be  integrated  through  a  complete 
cycle.  Graphically  we  may  represent  such  a  power  as  in 
Fig.  3,  wherein  e  represents  the  sine  wave  of  varying  voltage 
values  for  a  single  period  and  i  the  varying  ampere  values 
for  the  same  period  in  phase  with  the  voltage.  The  curve 
p  then  represents  the  varying  power  values,  and  is  obtained 
by  multiplying  the  corresponding  ordinates  of  the  voltage 
and  current  curves. 

17 


18  AMERICAN  METER  PRACTICE. 

The  product  of  the  mean  effective  volts  and  amperes 
gives  the  mean  effective  watts  passing  in  the  circuit  or  the 
mean  value  of  the  power  curve  p,  hence,  for  all  non-in- 
ductive circuits,  Pe= true  watts. 

If  the  current  flowing  in  curve  i  be  passed  through  a  coil 
of  wire  and  another  coil  be  energized  by  a  current  pro- 
portional to  and  varying  with  the  voltage  curve  e,  the  two 
coils,  if  so  placed,  will  form  a  resultant  magnetization  for  any 
instant  of  time  proportional  to  the  product  of  the  instanta- 
neous values  of  e  and  i  or  the  watts  passing  in  the  circuit. 

If  a  movable  member  or  armature  be  provided,  of  such 
character  that  it  is  moved  by  the  operation  of  this  resultant 
magnetization  in  such  manner  that  its  speed  is  propor- 
tional to  the  watts  passing  in  the  circuit,  a  record  of  the 
power  passing  is  obtained.  In  recording  the  flow  of 
alternating  current  energy  this  principle  has  been  used  in 
the  development  of  two  classes  of  meters,  which  for  con- 
venience are  styled  inductive  and  non-inductive. 

A  non-inductive  meter  can  be  used  for  either  direct  or 
alternating  current.  A  familiar  type  is  the  Thomson 
recording  wattmeter.  In  this  type  of  meter  the  field 
coils  are  in  series  with  the  current  flowing,  the  shunt  field 
coils  are  energized  proportionately  to  the  voltage  of  the 
circuit,  and  the  torque  exerted  on  the  armature  is  for  any 
instant  proportional  to  the  product  of  the  instantaneous 
values  of  the  current  and  E.  M.  P.,  hence  the  mean  torque 
is  proportional  to  the  product  of  effective  volts  by  effective 
amperes,  or  the  true  watts  passing  in  the  circuit. 

The  method  of  connecting  this  meter  is  the  same  as  on 
direct  current  circuits,  and,  in  fact,  is  interchangeable  with- 
out recalibration,  the  error  being  for  practical  purpose 
inappreciable. 


MEASUREMENT  OF  POWER.  19 

The  induction  meter  is  either  a  "current"  meter  or 
wattmeter,  and  operates  by  means  of  a  "shifting"  field 
acting  on  a  closed  secondary  armature,  the  eddy  currents 
induced  in  the  armature  reacting  on  the  shifting  or  rotating 
field  in  such  manner  as  to  produce  a  torque  proportional  to 
the  energy  or  current  passing,  according  to  whether  it  is  a 
"current "  or  wattmeter. 

A  well-known  type  of  current  meter  is  the  Shallenberger 
in  which  the  series  current  passes  through  a  primary  coil 
set  at  an  angle  with  a  closed  secondary  within  it,  the  plane 
of  the  two  magnetizations  being  at  a  like  angle  and  differ- 
ing in  phase.  Mounted  in  inductive  relation  is  a  thin  disk 
armature  in  which  eddy  currents  are  generated  by  the 
shifting  or  rotating  field.  The  reaction  of  these  resultant 
fields  tends  to  revolve  the  armature,  the  torque  being 
proportional  to  the  square  of  the  current. 

A  fan  brake,  whose  retarding  effect  increases  as  the  square 
of  the  speed,  is  attached  to  the  spindle  on  which  the  arma- 
ture is  carried,  and  enables  the  meter  to  record  the  current 
flowing. 

In  the  wattmeter,  of  which  there  are  many  types,  the 
series  and  shunt  field  coils  are  wound  in  inductive  relation 
to  a  movable  closed  secondary  or  armature  in  which  eddy 
currents  are  induced  proportional  to  the  magnetizations 
set  up  in  the  series  and  shunt  field  coils.  The  shunt  field 
coils  are  displaced  in  phase  from  the  series  coils  by  having 
a  reactance  placed  in  series  with  them,  the  magnetizations 
thus  creating  a  shifting  or  rotating  resultant  field. 

The  field  set  up  by  the  induced  eddy  currents  in  the  re- 
volving secondary  lags  behind  the  resultant  field  set  up  by 
the  series  and  shunt  field  coils,  creating  a  torque  on  the 
secondary  which  is  proportional  to  the  square  of  the 
energy  flowing.  The  providing  of  a  brake,  whose  retarding 


20 


AMERICAN  METER  PRACTICE. 


force  varies  as  the  square  of  the  speed,  enables  the  energy 
passing  to  be  obtained  from  the  speed  of  the  revolving 
spindle  to  which  the  armature  is  attached.  There  are 
many  variations  and  different  arrangements  of  the  fore- 
going general  principles. 

The  power  passing  in  an  inductive  single-phase  circuit 
may  be  graphically  illustrated  by  Fig.  4,  wherein  the 
current  lags  behind  the  voltage  by  60°. 


FIG.  4. 


The  resultant  power  curve  p  represents  the  watts  passing 


/?    A 


in  the  circuit,  and  is  written  Pe  =  —  cos. 


angle  of  lag. 

The  power  passing  in  an  alternating  circuit  at  any 
instant  is  equal  to  the  product  of  the  instantaneous  values 
of  the  current  and  voltage,  etc.  (see  American  Electrician, 
March,  1902),  and  acts  as  a  generator  for  a  portion  of  each 
period,  the  useful  power  being  the  difference  between 
positive  and  negative  values  of  the  curve  p. 

The  resultant  torque,  therefore,  exerted  on  the  coils  of  a 
meter  in  circuit  with  an  inductive  load  is  not  proportional 
to  the  product  of  the  virtual  volts  and  virtual  amperes  as 
measured  by  an  indicating  instrument,  but  to  this  product 
multiplied  by  the  power  factor  of  the  circuit;  the  power 
factor  is  the  ratio  between  the  true  and  apparent  watts. 


MEASUREMENT  OF  POWER.  21 

In  the  metering  of  three-wire  single-phase  systems,  in- 
ductive or  non-inductive,  the  same  general  principles  out- 
lined in  the  foregoing  hold  true. 

Multiphase  systems  are  a  combination  of  single-phase 
systems  differing  in  phase  from  each  other,  and  are  used  in 
distributions  for  light  and  power  owing  to  the  ease  with 
which  motors  can  be  operated  thereon. 

The  systems  in  general  use  are  the  quarter-phase  and 
three-phase,  the  former  composed  of  two  single-phase 
circuits  differing  by  90°  and  distributed  by  either  four  or 
three-wires,  the  latter  of  three  single-phase  circuits  differing 
by  120°  and  distributed  by  either  four  or  three- wires. 

The  quarter-phase  system,  employing  four  wires  for  its 
distribution,  is  metered  exactly  as  two  separate  single- 
phase  circuits  would  be,  the  total  power  in  the  two-phases 
being  the  sum  of  the  energy  components  of  each  phase. 
When  the  two  phases  are  balanced,  that  is,  have  the  same 
amount  of  energy  passing  in  each  phase,  it  is  only  neces- 
sary to  meter  one  phase  and  multiply  the  result  by  two  to 
get  the  total  amount  of  energy  passing.  When  the  phases 
are  unbalanced,  that  is,  have  different  loads  on  each  phase, 
two  meters  are  necessary,  one  in  each  phase,  to  register  the 
energy  passing. 

In  the  commercial  distribution  of  this  system  it  is  the 
usual  practice  to  take  a  lighting  circuit  into  a  customer's 
premises  from  one  phase  only  and  a  power  circuit  from 
both  phases.  The  motor  furnishes  a  balanced  load  and 
needs  only  one  meter  and  the  lights  one  meter.  In  this 
way,  by  loading  up  the  phases  equally,  the  number  of 
meters  needed  for  metering  the  lights  can  be  kept  down 
to  one  meter  per  customer. 

When  three  wires  are  used  in  the  distribution  of  two- 
phase  currents,  one  wire  acts  as  a  common  return  for  the 


22 


AMERICAN  METER  PRACTICE. 


other  two,  and  the  instantaneous  value  of  the  current  on 
the  common  return  at  any  instant  is  the  algebraic  sum  of 
the  instantaneous  values  of  the  currents  of  each  phase. 

The  virtual  resultant  value  would  be  the  hypothenuse 
of  a  right  triangle  which  would  represent  the  current  in 
phase  and  value.  The  resultant  voltage  is  found  in  the 
same  way,  hence  the  virtual  watts  would  be  the  product 
of  the  resultant  current  by  the  resultant  voltage  for  a  non- 
inductive  circuit. 

As  an  example,  suppose  we  have  a  two-phase  system 
carrying  10  amperes  in  each  phase  at  a  voltage  of  100  v., 


10  Amp. 


TO.  V. 


FIG.  5. 


FIG.  6. 


the  triangle  of  the  current  values,  Fig.  5,  would  give  a 
resultant  amperage  of  14.14,  the  triangle  of  the  voltage 
values,  Fig.  6,  gives  a  resultant  voltage  of  141.4  volts. 
The  total  watts  passing  in  the  circuit  is  the  product  of 
these  two  resultants,  or  a  watt  value  of  2,000  watts. 

Calculating  the  watts  separately  for  each  phase  we  have 
10  amp.,  x  100  v.  =  1000  watts  (i) 
10  amp.,  x  100  v.  =  1000  (2) 

2000  watts 
which  is  the  same  as  the  above. 


MEASUREMENT  OF  POWER. 


23 


The  resultant  voltage  and  resultant  amperes  being  the 
•same  in  phase  when  the  load  is  balanced,  a  meter,  Fig.  7, 
with  its  series  field  coils  placed  in  the  common  return  and 


FIG.  7. 

its  shunt  field  coils  energized  by  the  resultant  voltage  of  the 
system,  would  give  the  true  power  passing  in  the  circuit. 

When  the  load  is  unbalanced  the  resultant  ampere  value 
leads  or  lags  behind  the  resultant  voltage  of  the  system 
and  may  be  displaced  in  phase  either  way  by  45°  on  non- 
inductive  load.  The  true  power  in  the  circuit  is  then 
obtained  by  multiplying  by  the  cosine  of  angle  of  lag  or 
lead. 


FIG.  8. 


As  a  wattmeter  records  the  product  of  the  instantaneous 
values  and  not  the  maximum  values  of  current  and  voltage, 
the  record  is  a  true  one  of  the  energy  passing  in  the  circuit. 


24 


AMERICAN  METER  PRACTICE. 


This  connection,  Fig.  7,  will  not  record  the  true  power 
passing  on  an  unbalanced  inductive  circuit,  as  an  angle  of 
lag  or  lead  of  45°  could  give  a  wattless  register,  allowing 
70  per  cent,  of  the  energy  passing  to  remain  unrecorded. 
On  balanced  circuits,  however,  feeding  induction  motors, 
this  connection  readily  takes  the  place  of  the  two  meters 
shown  in  Fig.  8,  where  the  series  field  coils  are  connected 
in  the  outside  legs  of  the  circuit  and  the  potential  circuit  fed 
between  the  given  leg  in  the  meter  and  the  common  return. 

When  the  induction  type  of  meter  is  used,  the  potential 
circuit  is  so  connected  as  to  differ  in  phase  from  the 
A 


FIG.  9. 

series  field  circuit  by  90°,  hence  in  Fig.  8  the  potential 
circuit  for  each  meter  would  be  fed  from  the  given  leg  in  the 
meter  to  the  other  outside.  This  is  the  connection  most 
commonly  used  in  metering  two-phase  circuits.  The 
elements  of  two  meters  are  often  combined  under  one 
cover  to  act  on  a  common  armature.  The  elements  are 
connected  in  the  same  manner  as  though  they  were  separate 
meters,  and  need  not  be  further  elaborated. 


MEASUREMENT  OF  POWER. 


25 


Three-phase  circuits  are  connected  in  "star"  or  "delta" 
grouping;  the  former  sometimes  uses  four  wires  in  the  dis- 
tribution while  the  latter  is  always  distributed  by  means  of 
three  wires. 

In  Fig.  9,  the  "star"  grouping  with  common  centre  at  o 
is  shown,  the  voltage  of  the  three  legs  being  represented 
in  intensity  and  phase  by  the  lines  a,  6,  c.  The  resultant 
voltage  of  such  a  system  for  any  instant  of  time  may  be 
found  graphically  by  producing  the  single-leg  of  opposite 

D 


FIG.  10. 

sign  to  the  other  two  backwards,  and  finding  the  resultant 
by  the  parallelogram  of  forces.  The  diagonal  will  represent  in 
sign  and  phase  the  resultant  of  the  voltage  on  the  three  legs. 
In  Fig.  10  the  resultant  is  \J '3  times  the  voltage  of  one 
phase  and  leading  it  by  30°.  If  one  phase  be  selected  as  the 
leading  one,  the  resultant  voltage  will  be  found  to  be  always 
leading  it  by  30°.  In  the  same  Fig.  10  in  a  balanced 
circuit  the  current  will  have  a  resultant  coinciding  with 


26  AMERICAN  METER  PRACTICE. 

the  voltage  resultant,  and  the  product  of  the  two  resultants 
will,  for  non-inductive  load,  represent  the  true  power 
passing. 

The  algebraic  sum  of  the  resultants  of  the  voltage  taken 
consecutively  between  the  three  legs  of  a  system  will  equal 
for  any  instant  the  resultant  positive  or  negative  value  of 
the  voltage  at  that  instant.  Likewise,  the  resultant  of  the 
current  flowing  for  any  instant  is  the  algebraic  sum  of  the 
three  resultant  currents  of  the  system  found  in  like  manner. 
Therefore,  the  current  passing  over  any  two  legs  of  a  three- 
wire  three-phase  circuit  is  the  algebraic  sum  of  the  three 
resultant  currents  of  the  system,  hence  the  power  passing 
in  the  circuit  is  the  product  of  the  resultant  current  and 
voltage.  The  algebraic  product  of  two  minus  quantities  is 
always  a  plus  quantity,  hence  the  power  passing  is  always 
positive  in  character  on  non-inductive  circuits.  On  in- 
ductive circuits,  where  the  current  leads  or  lags  behind  the 
voltage,  a  minus  quantity  of  current  flows  for  a  portion  of 
each  period. 

Some  simple  rules  deduced  from  the  above  may  be  of 
service  in  readily  computing  the  energy  passing  in  poly- 
phase systems. 

In  "star"  or  "Y"  connected  systems,  or  any  system 
employing  a  common  neutral,  the  resultant  voltage  is 
equal  to  the  effective  voltage  X  \/m,  m  being  the  number 
of  phases.  The  resultant  amperes  flowing  in  any  system  is 
the  average  of  the  sum  X  \fm-  The  energy  passing  is, 
therefore,  the  common  resultant  voltage  X  common  re- 
sultant amperage  X  cos.  tp  or  lag  angle.  Suppose,  for 
example,  the  amperes  in  the  different  legs  of  a  three-phase 
unbalanced  system  are  10,  20  and  30  respectively,  and  the 
effective  volts  of  the  circuit,  taken  with  regard  to  a  common 
neutral  point  or  conductor,  100  volts.  The  average  value 


MEASUREMENT  OF  POWER.  27 

of  the  amperes  is  20,  and  the  resultant  is  20  X  \/3==34-^ 
amperes.  The  resultant  voltage  is  100  X  v/3~==I73  v°lts. 
The  cosine  of  angle  of  lag  q>  is  taken  as  .5,  corresponding 
to  an  angle  of  60°. 

The  energy  passing  in  such  a  circuit  is  34.6  amperes 
X  173  volts  X  .5  =  3000  watts.  The  same  result  is  ob- 
tained by  taking  each  leg  separately,  multiplying  a-mperes 
X  effective  volts  X  cosine  q>  =  60  amperes  X  100  V. 
•5  X3OO°  watts. 

The  common  neutral  point  or  conductor  is  not  always 
available,  hence  the  advantage  of  the  first  method  where 
in  practice  the  resultant  voltage  is  the  voltage  between 
any  two  lines. 

Where  the  current  lag  angles  in  the  different  branches  of 
the  circuit  are  of  different  values  the  resultant  amperes 
can  be  plotted  graphically,  or  the  energy  of  each  leg  com- 
puted by  multiplying  the  apparent  watts  found  by  the 
power  factor,  and  adding  the  amounts  thus  obtained  to 
get  the  total  energy  of  the  circuit. 

When  the  neutral  point  of  a  star  connected  system  is 
extended  to  the  distribution,  the  system  becomes  three 
independent  circuits  with  a  common  neutral,  the  algebraic 
sum  of  the  currents  on  the  neutral  for  any  instant  being 
zero. 

The  energy  in  a  three-phase  circuit  may  be  measured  by 
one,  two  or  three  meters,  or  their  equivalent,  of  inductive 
or  non-inductive  type. 

The  non-inductive  type  of  meter  has  maximum  torque 
when  the  shunt  field  coils  and  series  field  coils  are  in 
phase.  Therefore,  as  the  lag  angle  increases  the  torque 
diminishes,  until  at  quarter-phase  the  torque  is  zero. 
Hence,  it  is  impossible  in  meters  of  this  character  to  com- 
bine series  fields  of  different  phases  to  act  in  conjunction 


28  AMERICAN  METER  PRACTICE. 

with  shunt  field  coils  in  phase  with  only  one  of  them  to 
measure  the  energy  passing.  The  case  where  only  one 
meter  is  used  to  measure  unbalanced  polyphase  energy 
factors  is  confined  to  meters  of  the  inductive  type  where 
one  or  more  measuring  elements  are  combined  to  give  a 
resultant  measuring  value  to  a  common  movable  armature. 
In  Fig.  n,  let  A  B  C  represent  a  three-phase  relation 
feeding  circuit  having  a  balanced  load,  the  series  coils  of  a 
meter  D  are  then  placed  in  either  one  of  the  three  legs  and 
the  shunt  field  coil  fed  by  the  virtual  voltage  of  the  system 


FIG.  11. 

obtained  from  a  star  connected  set  of  resistances  having  a 
common  neutral  point.  This  connection  applies  to  either 
star  or  mesh  groupings.  The  register  of  the  meter  is 
multiplied  by  three  to  obtain  the  total  power  flowing  in  the 
circuit.  That  is,  the  power  passing  in  each  leg  of  the  circuit  is 


In  this  instance  Fig.  n  represents  the  connection  for  a 
non-inductive  type  of  meter.  If  an  inductive  meter  be 
used  the  series  and  shunt  field  coils  must  be  displaced  90° 
in  phase,  and  the  meter  fed  as  shown  in  Fig.  12,  wherein  the 
potential  circuit  is  fed  between  C  B  whose  resultant  voltage 
lags  90°  behind  current  in  A. 


MEASUREMENT  OF  POWER. 


29 


One  meter  is  sufficiently  accurate  for  balanced  three- 
phase  loads,  but,  when  the  load  becomes  unbalanced,  two 
legs  of  the  circuit  must  be  metered. 

If  non-inductive  meters  be  employed  we  connect  them 
as  shown  in  Fig.  13,  where  the  current  in  A  lags  on  non- 


FIG.  12. 

inductive  load  30°  behind  the  voltage  in  shunt  coil  d\  like- 
wise, current  in  b  lags  30°  behind  the  voltage  in  e.  The  sum 
of  the  two  registers  of  the  meter  is  equal  to  the  resultant 
voltage  of  the  system  by  the  resultant  amperes.  If  the 
current  be  inductive,  the  current  in  a  lags  cos.  (<p  -f  30°) 


FIG.  13. 


behind  the  voltage;  likewise,  current  in  b  lags  cos.  (<p  -  30°) 
behind  the  voltage  in  e.  In  other  words,  the  true  watts  equal 
the  resultant  current  X  resultant  voltage  X  cos.  <p.  The 
power  passing  is  equal  to  the  algebraic  sum  of  the  two 


30 


AMERICAN  METER  PRACTICE. 


registers.  It  is  easily  seen  that  when  <p  =  60°,  the  expression 
cos.  (cp  +  30)  is  equal  to  cosine  90°,  which  gives  a  wattless 
register.  Under  such  conditions  one  meter  registers  the 
total  current.  If  the  lag  angle  be  greater  than  60°  one 
meter  runs  backward. 

Instead  of  the  two  meters  just  shown  in  Fig.  13,  one 
inductive  meter  may  be  used  which,  in  general,  consists  of 
two  elements  combined  under  one  cover,  in  short,  two 
single-phase  meters  so  arranged  with  regard  to  a  common 
armature  that  the  power  passing  is  recorded  on  a  single 


FIG.  14. 

dial  train.  There  are  many  types  of  this  meter,  but  in 
principle  they  bear  sufficient  resemblance  to  the  one  shown 
diagrammatically  in  Fig.  14  for  it  to  represent  them. 

A  is  a  closed  secondary  or  armature  in  inductive  rela- 
tion to  the  series  and  shunt  field  coils  H,  H',  S,  S',  being 
displaced  in  phase  by  90°.  The  maximum  torque  is  there- 
fore exerted  when  the  phase  displacement  is  90°,  and 
diminishes  as  the  angle  decreases,  becoming  zero  when  the 
two  circuits  are  in  phase.  This  is  the  condition  of  the 
circuit  having  a  lag  of  90°  or  wattless  current. 

This  action  is  just  the  opposite  of  the  action  in  the  non- 
inductive  meter,  where  the  torque  diminishes  as  the  series 
and  shunt  field  coils  become  displaced  in  phase.  The 


MEASUREMENT  OF  POWER. 


torque  of  both  meters  varies,  however,  with  the  cosine  law,, 
but  in  opposite  directions.  Mesh  connected  systems  are 
metered  in  the  same  manner;  in  fact,  the  three-wire  two- 
phase  Y  and  mesh  connections  three-phase  are  all  metered 
alike. 

D 


The  metering  of  such  systems  as  the  monocyclic  is 
worked  out  along  the  same  general  lines,  but  presents  some 
peculiarities  which  are  interesting. 

In  the  monocyclic  system  a  regular  single-phase  circuit 
is  used  in  conjunction  with  a  third  wire  called  the  teaser, 
which  differs  from  the  single-phase  circuit  by  90°  in  phase. 


FIG.  16. 

In  the  generator,  one  end  of  the  teaser  coil  is  tapped  on 
to  the  middle  of  the  single-phase  coil,  and  the  other  end 
leads  to  a  collecting  ring.  The  relation  of  the  E.M.F.  in 
the  resulting  three-wire  circuit  may  be  illustrated  diagram- 
matically  in  Fig.  1 5 ,  wherein  A  C  is  voltage  of  single-phase, 
B  its  middle  joint,  D  B  teaser  winding,  A  D  and  D  C  the 
resultant  E.M.F.  between  the  two  wires  and  the  teaser. 


32  AMERICAN  METER  PRACTICE. 

Such  a  system  is  adapted  to  the  distribution  of  light  and 
power,  the  lights  being  connected  to  the  single-phase  in 
the  usual  way,  and  the  motors  as  illustrated  in  Fig.  16. 

As  indicated,  the  primaries  of  the  two  transformers  are 
placed  in  series  with  the  teaser  connected  to  the  point  of 
joining.  The  secondaries  are  cross  connected,  forming  a 
resultant  lop-sided  three-phase  relation  which  is  used  to 
operate  a  three-phase  motor  in  the  same  manner  that  a 
regular  three-phase  system  would  do. 

Another  way  of  connecting  up  two  transformers  to  accom- 
plish the  same  results  is  illustrated  in  Fig.  17,  wherein  a 
small  transformer  is  shown  connected  between  the  teaser 


Motor 


FIG.  17. 

and  the  middle  point  of  the  large  transformer,  the  relation 
of  the  current  in  the  secondaries  then  being  the  same  as 
in  the  generator. 

To  meter  the  power  passing  in  the  connection  Fig.  16, 
we  proceed  exactly  as  in  unbalanced  three-phase  systems, 
or  two-phase  systems  employing  a  common  return.  Hence, 
with  non-inductive  meters  we  place  one  in  each  outside 
leg  and  feed  the  potential  circuit  between  the  given  leg 
and  common  return. 

With  inductive  meters  the  regular  polyphase  meter  used 
for  three  and  two-phase  systems  is  placed  in  circuit.  As 
we  have  pointed  out,  this  meter  usually  consists  of  two 


MEASUREMENT  OF  POWER.  33 

elements  combined  under  one  cover  and  acting  on  a  com- 
mon armature. 

When  a  service  consisting  of  motor  and  lights  is  fed  from 
the  connection  shown  in  Fig.  17,  the  proper  registration  of 
the  energy  passing  is  accomplished  by  using  two  non-induc- 
tive meters  connected  as  shown  in  Fig.  31,  Chap.  VI,  or  a 
polyphase  induction  meter  so  designed  as  to  have  one  of 
its  elements  connected  in  circuit  with  the  teaser  circuit 
as  outlined  diagrammatically  Fig,  31,  Chap,  VI. 


CHAPTER  III. 

Meter  Selection — Requisites  of  a  Good  Meter — Commercial 
Considerations. 

Considerations  other  than  cost  render  the  selection  of 
the  best  meter  a  difficult  task,  owing  to  the  various  classes 
of  service  to  be  provided  for.  In  commercial  distributions 
of  current  we  have  incandescent  lamps,  arc  lamps  and 
motors  to  meter  beside  other  forms  of  energy  consumers, 
such  as  electric  heaters,  etc.  Frequently  all  of  these  forms 
of  translating  devices  are  found  in  one  installation,  and  it 
is  desirable  to  meter  them  through  one  meter.  The  current 
may  be  direct  or  alternating,  or  both,  and  the  various 
conditions  that  the  meter  has  to  meet  will  be  treated 
separately. 

First.     Varying  Voltage  and  Load. 

If  a  constant  load  at  a  constant  voltage  always  passed 
through  the  meter,  its  calibration  would  be  a  simple  matter, 
but,  in  the  majority  of  installations,  the  variation  is  between 
the  limits  of  an  eight  c.  p.  lamp  and  the  full  capacity  of 
the  meter.  The  meter  must  record  the  true  watts  passing 
at  all  loads,  and  its  accuracy  on  light  loads  is  extremely 
important.  It  is  seldom  that  a  good  meter  cannot  be 
relied  upon  to  record  its  full  load  within  one  or  two  per 
cent,  of  its  correct  value,  but  this  same  meter  may  be  50 
per  cent,  slow  on  light  loads  and  fail  to  record  at  all  on  an 
eight  c.  p.  lamp.  In  large  systems  of  distribution  the 
voltage  remains  very  constant,  but  in  outlying  districts, 

34 


METER  SELECTION.  35 

and  in  small  plants  with  insufficient  copper  in  the  lines,  the 
voltage  often  varies  ten  per  cent,  either  way  from  its 
normal  value.  The  meter  must  record  accurately  under 
these  variations  of  voltage.  Light  load  accuracy  has  a  far 
reaching  effect  on  the  earning  capacity  of  the  plant,  and 
is  so  important  that  it  is  taken  up  more  fully  in  Chapter 
VIII. 

Second.     Varying  Frequency. 

Only  in  a  few  of  the  larger  plants  are  the  alternating 
generators  operated  in  parallel,  and  in  many  of  the  smaller 
plants  it  is  often  the  case  that  two  circuits  from  different 
machines  may  vary  ten  per  cent,  in  frequency,  owing  to 
different  speeds  of  the  generating  units.  Meters  in  service 
are  often  called  upon  to  register  at  slightly  different 
frequencies  from  the  one  they  are  designed  for.  This 
irregularity  may  also  be  caused  by  the  varying  frequency 
of  a  circuit  caused  by  change  of  speed  of  the  generating  unit. 
The  meter  must  record  accurately  under  these  conditions 
the  total  watts  passing  in  the  circuit,  or  fail  to  meet  the 
requirements  of  commercial  service. 

Third.     Power  Factor. 

When  a  circuit  is  inductive  it  is  said  to  have  a  power 
factor  or  a  ratio  of  the  true  to  the  apparent  watts  passing 
in  the  circuit.  Many  circuits  are  purely  inductive,  such  as 
those  feeding  induction  motors,  but  a  single  installation 
may  have  connected  incandescent  lamps,  or  non-inductive 
load,  as  well  as  arc  lamps  and  motors.  The  power  factor 
under  these  conditions  can  vary  from  .55  to  unity.  The 
meter  is  called  upon  to  register  accurately  throughout  this . 
range.  These  conditions  are  not  at  all  unusual,  but  are.- 
met  in  practice  every  day. 


36  AMERICAN  METER  PRACTICE. 

Fourth.     Sine  Wave  Form. 

The  changes  of  direction  of  alterations  of  a  current  vary 
in  intensity  from  positive  to  negative  according  to  the  sine 
law.  The  variation  approaches  the  true  sine  wave,  but 
many  wave  forms  met  in  practice  are  jagged,  peaked  or 
flat.  A  meter  for  commercial  use  must  fit  any  wave  form; 
that  is,  record  as  accurately  on  one  form  as  another. 

Fifth.     Short  Circuits. 

The  effect  of  a  short  circuit  on  a  meter  is  one  that  should 
be  carefully  determined.  The  instantaneous  rush  of  current 
is  great  and  creates  a  strong  magnetic  field  which  extends 
to  the  permanent  magnets  and  tends  to  demagnetize  them 
unless  a  shield  is  interposed  between  them.  This  shield 
may  be  of  iron,  but  a  closed  secondary  band  is  sometimes 
placed  around  the  field  coil  which  sets  up  a  counter  magnetic 
iield  when  a  short  circuit  takes  place.  Another  effect  of 
:short  circuit  on  meters  where  a  disk  or  drum  armature  is 
msed  is  to  distort  or  bend  the  disk  by  the  powerful  moment- 
ary thrust  exerted  which  acts  exactly  like  a  blow.  This 
is  prevented  in  some  meters  by  evenly  distributing  the 
field  coils  in  such  a  way  as  to  balance  this  thrust. 

Sixth.     Permanency  of  Magnetic  Drag. 

If  the  meter  stand  successfully  the  short  circuit  test 
without  affecting  the  permanence  of  the  magnets,  it  is 
proof  against  immediate  deterioration,  but  the  action  of 
time  may  still  be  detrimental.  Some  essentials,  however, 
of  correct  form  and  mode  of  manufacture  will  be  of  service 
in  judging  the  magnets.  A  very  hard  steel,  usually  an 
alloy  of  tungsten,  is  highly  tempered  and  magnetized  by 
contact  with  powerful  electro  magnets  and  partially  de- 
magnetized by  weak  alternating  current  magnetizations. 


METER  SELECTION.  37 

This  process  is  repeated  until  the  steel  is  brought  to  a  state 
of  permanent  magnetization.  This  state  of  permanent 
magnetization  has  been  determined  by  experiment,  and 
each  manufacturer  knows  from  the  quality  of  steel  used 
just  the  balancing  line  where  the  magnets  will  not  lose  or 
gain  in  magnetism.  Conditions  of  length  and  area  and 
length  of  air  gap  affect  permanence.  The  magnet 
should  be  long  and  the  pole  pieces  of  sufficient  area  to  allow 
of  a  good  distribution  of  the  magnetic  flux.  The  length 
of  the  air  gap  should  be  small,  otherwise  the  magnetic  flow 
is  retarded  and  the  magnet  is  unable  to  maintain  perma- 
nently a  flow  across  the  gap. 

Where  the  magnets  have  been  forged,  the  manufacturer 
usually  lets  them  set  to  assume  their  final  shape.  Even 
then  the  distance  between  the  poles  may  change  slightly 
and  the  accuracy  of  the  meter  be  destroyed.  Any  meter, 
therefore,  which  combines  long  magnets,  short  air  gap  and 
permanently  fixed  pole  pieces  has  an  advantage  over  one 
lacking  these  points. 

Seventh.     Torque. 

The  torque  of  a  meter  is  directly  proportional  to  its 
efficiency  as  a  motor.  In  other  words,  suppose  between  the 
shunt  and  field  losses  it  takes  ten  watts  to  operate  the 
meter.  These  ten  watts  are  the  input  into  the  motor  meter, 
and  the  efficiency  of  this  motor  meter  will  give  the  ratio 
of  the  torque  exerted  on  the  armature.  A  good  meter,  then, 
should  be  as  highly  efficient  a  motor  as  possible  to  enable 
the  losses  to  be  made  as  small  as  is  compatible  with 
efficiency. 

When  we  consider  the  counter  frictional  torque  of  a 
meter,  the  value  of  having  the  current  torque  as  large  as 
possible  is  immediately  apparent.  The  torque  of  a  meter 


38  AMERICAN  METER  PRACTICE. 

is  also  its  measure  of  ability  to  overcome  friction,  namely, 
if  the  ratio  of  frictional  and  current  torque  be  i  to  100,  the 
doubling  of  the  friction  would  only  cause  a  loss  of  one  per 
cent,  additional,  whereas,  if  the  ratio  were  i  to  10,  an  ad- 
ditional loss  of  ten  per  cent,  would  be  experienced  when 
the  friction  is  doubled.  Hence,  the  securing  of  as  large  a 
torque  as  possible,  without  too  great  energy  losses,  is  a 
matter  of  careful  design  and  of  extreme  importance. 

Eighth.     Friction  and  Friction  Balancing. 

The  support  of  the  armature  and  the  dial  train  are  the 
points  of  friction  in  a  meter,  and  in  many  meters  are 
balanced  by  an  initial  turning  impulse  imported  to  the 
armature.  The  turning  impulse  remains  constant,  but  the 
frictional  equivalent  is  continually  varying,  not  only  in  one 
location,  but  for  various  locations  of  the  meter.  As  this 
friction  changes  with  wear,  we  find  the  meters  creeping  in 
some  localities  and  very  slow  in  others,  owing  to  the  vary- 
ing degrees  of  vibration  present.  Many  forms  of  friction 
balance  are  used,  but  none  are  perfect,  and  the  true  solu- 
tion of  the  problem  lies  in  reducing  the  counter  frictional 
torque  to  a  minimum  and  raising  the  current  torque  to  a 
maximum,  so  that  the  error  due  to  friction  is  inappreciable. 
In  selecting  a  meter,  therefore,  a  careful  determination  of 
this  ratio  is  all  important. 

Ninth.     Energy  Losses. 

Work  cannot  be  done  without  consumption  of  energy, 
and  a  balancing  ratio  between  the  energy  needed  and  the 
torque  desired  must  be  reached  in  the  determination  of  the 
allowable  losses  in  the  meter. 

The  loss  in  the  potential  circuit  ranges  from  i  J  to  15 
watts  in  different  makes  of  meters.  Only  a  part  of  the 


METER  SELECTION.  3D 

energy  is  available  for  useful  work ;  the  remainder  is  given 
off  in  heat.  The  field  losses  vary  with  the  load,  but  should 
never  exceed  one  per  cent,  of  the  rated  capacity  of  the 
meter  on  full  load. 

Large  losses  in  the  shunt  and  field  circuits  are,  in  poorly 
designed  meters,  not  compensated  for  by  a  resulting  large 
torque,  or  in  other  words,  the  efficiency  of  the  motor  meter 
is  very  low.  The  determination  of  this  efficiency  is  easily 
made  by  measuring  the  pull  of  the  disk  by  means  of  a 
sensitive  spring  balance  when  a  given  load  is  on  the  meter. 
The  reduction  of  the  watt  losses  of  the  meter  to  their 
mechanical  equivalent  at  the  point  of  attachment  of  the 
spring  balance  will  give  the  ratio  between  the  actual  work 
done  and  the  energy  consumed.  The  meter  possessing  the 
highest  efficiency  and  largest  torque  has  a  much  better  chance 
of  remaining  permanently  accurate,  provided  its  counter 
frictional  torque  is  lower  than  in  one  that  is  less  powerful. 

Tenth.     Armature  Support  and  Vibration. 

The  critical  point  in  the  permanence  of  the  constants 
of  a  meter  is  the  insurance  of  a  permanent  non-frictional 
support  for  the  armature.  Much  time  and  money  have 
been  expended  in  this  development,  and  the  two  outcomes 
are  a  highly  polished  jewel,  on  which  runs  the  hardened 
steel  point  of  the  armature  spindle,  and  magnetic  flotation 
of  the  armature. 

The  jewel  and  hardened  steel  point  can  hardly  be  called 
a  permanent  solution  of  the  problem,  as,  under  certain  con- 
ditions, the  jewel  wears  and  breaks  down  very  rapidly, 
destroying  at  the  same  time  the  smoothness  of  the  steel 
shaft. 

The  causes  of  jewels  breaking  down  are  vibration  and 
dust.  It  is  almost  impossible  to  eliminate  vibration  of  the 


40  AMERICAN  METER  PRACTICE. 

meter  support  in  some  locations.  The  passing  of  cars  and 
wagons,  and  heavy  jars  given  to  the  building,  jolt  the  meter, 
causing  the  armature  shaft  to  strike  a  blow  on  the  jewel 
which  frequently  cracks  and  very  quickly  destroys  its 
polished  surface.  On  alternating  current  circuits  the 
process  is  even  more  disastrous  in  its  final  results.  The 
slight  vibration  or  tremor  in  the  armature  drum  or  disk 
imparted  to  it  by  the  shunt  winding,  which  is  always  in 
circuit,  hammers  the  jewel  at  the  rate  of  the  alternations 
of  the  service  circuit.  The  millions  of  minute  blows  gradu- 
ally destroy  the  smoothness  of  the  jewel  and  it  finally 
breaks  down.  Magnetic  flotation  of  the  armature  not 
only  cures  this  evil,  but  reduces  the  initial  friction  of  the 
meter  to  a  large  extent.  The  armature  is  floated  in  space 
by  means  of  a  permanent  magnetic  system,  and  any  vibra- 
tion which  produces  a  lateral  thrust  has  no  effect  on  the 
meter.  A  meter  possessing  magnetic  flotation  of  the 
armature  and  fulfilling  the  previous  conditions,  if  it  meet 
the  requirements  of  the  service,  comes  nearer  the  ideal 
conditions  than  any  other. 

The  presence  of  dust  or  grit  in  the  meter  grinds  the 
polish  off  the  jewel  and  quickly  wears  it  out.  In  magnet- 
ically floated  armature  guides  this  dust  would  be  even  more 
disastrous. 

Eleventh.     Air  Tight. 

To  keep  out  dust,  insects,  acid  fumes  and  all  foreign 
matter  the  meter  must  be  air-tight.  The  carelessness  of 
meter  manufacturers  in  this  respect  has  been  appalling, 
but  the  responsibility  for  this  defect  rests  ultimately  upon 
the  meter  buyer,  as  he  should  insist  on  this  point. 

In  order  that  the  meter  may  retain  its  calibration  it  must 
have  the  same  conditions  present  in  service  that  it  had  when 


METER  SELECTION.  41 

installed,  and  the  exclusion  of  all  matter  which  can  in  any 
way  change  the  relation  of  the  different  elements  to  each 
other  must  be  insured. 

Twelfth.     Temperature  Co-Efficient. 

The  temperature  co-efficient  should  be  unity  through  a 
wide  range.  The  range  of  temperature  over  which  meters 
work  during  a  year's  service  is  as  high  as  100°.  Meters 
tested  hot  and  cold  often  show  as  much  as  five  per  cent, 
difference  in  their  reading,  owing  to  the  different  resistance 
of  the  windings  at  different  temperatures. 

Thirteenth.     Insulation. 

The  failure  of  many  meters  is  caused  by  defective  insula- 
tion. A  meter  is  easily  tested  for  insulation,  and  should 
be  rejected  unless  it  can  show  several  megohms  between  the 
windings  and  meter  frames. 

Fourteenth.     Mechanical  Features. 

An  eminent  engineer  once  said  that  if  a  machine  look 
right  it  is  almost  sure  to  be  right  in  design,  probably  draw- 
ing this  conclusion  from  a  sense  of  the  fitness  of  things.  All 
the  electrical  conditions  maybe  successfully  met  by  a  meter, 
but  its  mechanical  design  may  be  so  poor  as  to  make  it 
worthless.  Besides  the  elimination  of  friction  of  the  mov- 
ing parts,  it  is  an  important  consideration  that  the  general 
get-up  of  the  meter  should  be  pleasing  and  carefully  worked 
out.  Meters  receive  a  great  deal  of  handling,  and  fre- 
quently rough  handling.  The  mechanical  details  need  not 
be  elaborated,  but  the  proper  construction  of  the  meter 
frame  and  parts  should  be  worked  out  along  the  lines  of 
strength  and  rigidity  rather  than  lightness. 


42  AMERICAN  METER  PRACTICE. 

The  commercial  problems  involved  in  meter  selection  are 
complicated  by  reason  of  the  great  variety  of  service  fur- 
nished. Following  close  upon  the  determination  of  a  meter's 
electrical  and  mechanical  excellence  come  the  questions  of 
first  cost  and  operation,  which  vary  with  the  kind  of  service 
to  be  metered.  The  different  classes  of  service  which  may 
be  met  in  practice,  generated  and  sold  by  one  company,  are 
as  follows : 

1.  Plain  direct  current  two-wire  systems  of  115,  220  or 
500  volts. 

2.  Three-wire  direct  current    systems  of  115-230  and 
220—440  volts. 

3.  A  combination  of  either  one  or  two,  with  a  single- 
phase  two-wiring  alternating  current  system. 

4.  A  combination  of  either  one  or  two,  with  a  polyphase 
system. 

5.  Plain  single  or  polyphase  distributions  for  light  and 
power. 

6.  Series  arc  systems  in  conjunction  with  any  of  the 
above. 

Many  more  combinations  might  be  given,  but  the  above 
are  the  most  common  and  will  serve  as  illustrations.  To 
meet  the  first  case  a  two-wire  direct  current  meter  of 
either  the  chemical  or  motor  type  is  what  is  needed.  The 
most  extensively  used  meters  for  this  service  in  America 
have  been  the  Edison  chemical  meter  and  the  Thomson 
recording  wattmeter.  The  chemical  meter  is  rapidly 
passing  into  disuse.  In  principle  it  is  an  ampere  hour- 
meter  possessing  many  points  of  value,  but,  owing  to  the 
immense  amount  of  work  connected  with  its  operation,  it 
has  been  steadily  losing  ground  to  the  Thomson  or  corn- 
mutated  type  of  meter.  For  many  years  the  Edison 
chemical  meter  has  been  the  mainstay  of  direct  current 


METER  SELECTION. 

stations,  and,  when  carefully  operated,  furnished  a  very  ac- 
curate register;  in  fact,  in  many  instances  a  far  more 
accurate  record  can  be  obtained  with  it  than  with  any 
mechanical  meter.  An  incident  is  recalled  within  the 
writer's  experience  where  the  vibration  was  so  great  that 
special  screw  clips  were  designed  to  hold  the  bottles  in 
circuit,  the  conditions  being  such  that  any  mechanical 
meter  would  have  been  ruined  in  less  than  half  a  day. 

The  Thomson  and  Duncan  commutated  meters  are 
practically,  at  the  present  writing,  the  only  direct  current 
meters  in  use  in  America,  although  in  the  near  future  there 
promise  to  be  other  forms.  At  the  present  there  are  only 
two  selections  to  make,  either  the  chemical  or  commutated 
types.  Modern  practice  has  decided  in  favor  of  the  com- 
mutated type. 

The  second  case  falls  under  the  same  limitations  as  the 
first  and  may  be  dismissed  with  the  same  considerations. 

For  the  sake  of  simplification  we  will  confine  ourselves 
in  the  selection  of  the  best  meter  to  fulfill  the  conditions  of 
the  third  class  to  motor  types  of  meters. 

Here  we  have  a  varied  class  of  service,  direct  and  alter- 
nating current,  and  we  must  bear  in  mind  that  it  is  easier 
and  better  to  have  but  one  type  of  meter  in  service. 

Let  us  assume,  as  one  phase  of  case  three,  a  low  tension 
Edison  net  work  with  an  outlying  district  fed  by  alternat- 
ing current.  Then,  on  all  sides  where  the  two  districts  meet 
there  will  be  lapping  over  of  the  direct  and  alternating 
service.  If  two  types  of  meters  be  used,  which  are  not 
interchangeable,  the  meter  service  is  not  as  flexible  as  it 
would  otherwise  be.  It  would  also  necessitate  the  carry- 
ing of  a  much  larger  stock  of  meters  to  meet  all  demands. 
Again,  the  service  to  any  installation  could  not  be  changed 
from  direct  to  alternating  or  vice  versa  without  changing 


.44  AMERICAN  METER  PRACTICE. 

the  meter  as  well.  The  advantages  in  using  a  meter  com- 
mon to  both  systems  may  be  summed  up  as  follows: 

1 .  Flexibility  of  meter  service. 

2.  Carrying  of  a  smaller  stock. 

3.  Simplification  in  the  repair  and  testing  departments. 

4.  The  same  quality  of  meter  service  to  all  customers. 
Any  form  of  meter,  therefore,  which  will  operate  with 

equal  accuracy  on  direct  and  alternating  current  without 
any  change  in  calibration  would,  other  considerations  being 
equal,  be  the  proper  one  to  use. 

When  the  problem  is  further  complicated  by  having  a 
polyphase  system  to  meter  in  combination  with  a  direct 
current  system,  conditions  arise  which  have  to  be  carefully 
considered.  If  a  meter  having  an  armature  and  commu- 
tator is  used  for  the  direct  current  it  will  take  two  or  more 
meters  per  installation  to  meter  an  unbalanced  polyphase 
service,  so  that  the  first  cost  of  meters  must  be  taken  into- 
consideration,  that  is,  whether  it  is  cheaper  to  install 
two  meters  or  one  polyphase  induction  meter.  Other  con- 
siderations also  enter.  The  consumer  in  general  does  not 
understand  why  two  meters  should  be  put  in  to  register  a 
single  service,  and  no  amount  of  explanation  will  disabuse 
his  mind  of  the  idea  that  the  company  is  getting  the  better 
of  him.  Again,  the  maintenance  and  repairs  on  two  meters 
are  double  that  of  one  and  will  add  to  the  cost  of  operating 
the  meter  department.  These  considerations  outweigh 
those  advanced  for  the  use  of  one  type  of  meter,  and  it  is 
preferable,  in  this  case,  to  use  two  types  of  meters.  In  case 
five,  where  only  one  class  of  service  is  given,  namely,  a  single 
or  polyphase  distribution,  the  selection  of  a  meter  is  largely 
controlled  by  local  preference.  There  are  a  number  of 
meters  which  can  be  used  with  equal  success,  questions  of 
first  cost,  durability  and  small  maintenance  are  deciding; 


METER  SELECTION. 

factors,  and,  as  the  service  is  not  mixed,  it  is  best 

use  a  single  meter  per  installation.     It  is    frequently  the 

case  that  a  central  station  has  no  choice  in  the  selection  of 

its  meters ;  under  such  conditions  it  is  hard  to  work  out  a 

satisfactory  system  unless  the  meter  happens  to  be  a  good 

one. 

If  the  meter  selected  comply  with  both  the  electrical 
and  commercial  requirements  its  successful  operation  should 
be  assured  with  ordinary  care. 


CHAPTER  IV. 
Torque  and  Friction. 

The  designing  of  a  meter  for  permanent  commercial 
accuracy  involves  a  great  many  serious  problems.  In 
Chapter  III  we  have  alluded  to  the  principal  qualifications 
to  be  fulfilled  by  a  good  meter.  The  subject  of  torque  was 
treated  briefly,  but  its  true  significance  in  meter  design 
needs  fuller  elaboration. 

The  word  "torque"  is  used  to  express  the  force  with 
which  a  rotating  body  tends  to  revolve,  and  is  usually 
expressed  in  foot  pounds.  Counter  torque  is  a  force  acting 
in  opposition  to  torque;  thus,  the  friction  of  a  moving  body 
may  be  expressed  as  counter  torque,  the  overcoming  of 
which  consumes  a  certain  proportion  of  the  torque  of  the 
rotating  body.  In  a  meter  the  torque  is  a  minute  fraction 
of  the  foot  pound  unit,  and  the  counter  torque  or  friction  a 
smaller  quantity  still.  If  a  half  dozen  different  makes 
of  recording  wattmeters  be  set  up  and  tested  when  new, 
a  very  slight  difference  may  be  noticed  in  their  readings  on 
full  and  medium  loads,  but  very  decided  differences  are 
recorded  on  light  loads  from  five  per  cent,  and  under  of  the 
full  load  capacity.  In  other  words,  each  meter  has  a  differ- 
ent ratio  between  the  force  impelling  it  forward  and  the 
friction  of  the  moving  parts  holding  it  back.  The  friction 
in  each  meter  may  vary  widely,  and  the  impelling  force  or 
torque  may  do  the  same.  Consequently,  there  is  a  differ- 
ent ratio  between  friction  and  torque  for  each  individual 
meter. 

46 


TORQUE  AND  FRICTION.  47 

The  continued  accuracy  of  any  meter  depends  primarily 
on  preserving  permanently  the  ratio  between  torque  and 
counter-frictional  torque.  The  variable  quantity  in  this 
ratio  is  the  counter-frictional  torque;  hence,  the  torque 
should  be  so  large  in  proportion  that  a  doubling  or  trebling 
of  the  frictional  torque  would  have  no  appreciable  effect 
on  the  accuracy  of  the  meter.  For  example,  suppose  the 
ratio  existing  in  a  given  meter  on  a  given  load  be  i  to  100, 
then,  by  doubling  the  friction,  the  ratio  becomes  2  to  100. 
In  the  first  ratio  the  error  would  be  one  per  cent.,  in  the 
second,  two  per  cent.  On  the  contrary,  if  the  first  ratio 
on  the  same  load  were  i  to  10,  the  doubling  of  the  friction 
would  make  an  error  of  20  per  cent,  in  the  reading  of  the 
meter  instead  of  two  per  cent,  as  in  the  second  ratio. 
Carrying  on  this  process,  multiplying  each  friction  by  ten 
in  both  ratios  gives  a  ten  per  cent,  error  in  the  first  one  and 
a  complete  stoppage  of  the  meter  in  the  second.  If  the 
frictional  counter  torque  were  not  of  a  negative  character 
the  increasing  of  this  friction  in  the  second  ratio  above  ten 
would  result  in  a  reversal  of  the  meter.  In  speaking  of  the 
frictional  torque,  therefore,  we  have  to  think  of  it  as  a  neg- 
ative torque,  which  is  to  be  subtracted  from  the  current 
torque,  but  cannot  exert  its  influence  to  revolve  the  meter 
in  an  opposite  direction. 

The  current  torque  remains  constant  for  a  given  load  on 
the  meter,  but  necessarily  varies  with  the  load;  hence,  if 
the  ratio  be  i  to  10  on  ten  per  cent,  of  the  capacity  of  the 
meter,  it  becomes  i  to  100  on  full  load.  Therefore,  the 
percentage  by  which  the  meter  runs  slow  on  full  load  may 
be  read  as  a  multiplier  of  the  frictional  torque;  for  instance, 
eight  per  cent,  slow  means  an  increase  of  friction  of  eight 
times  the  original  amount.  It  is  assumed,  in  this  state- 
ment, that  the  meter  ran  properly  originally  and  became 


48  AMERICAN  METER  PRACTICE. 

slow  through  increase  in  friction.  Meters  can  run  slow 
from  other  causes,  but  these  causes  are  not  at  present  under 
discussion. 

In  order  to  present  more  clearly  the  ratio  of  current 
torque  and  counter-frictional  torque,  a  meter  of  five  amperes 
capacity  is  selected  for  illustration. 

For  the  sake  of  analysis  the  friction-torque  ratio  of  the 
meter  is  assumed  to  be  as  stated  in  the  second  column : 

Friction-Torque  Per  Cent. 

Load.  Ratio.  Slow. 

10  lamps       =100%  1-50  2% 

5     "  =    50%  1-25  4% 

2*   "  =    25%  1-12*  8% 

2        "  =     20%  I-IO  10% 

i      "  =    10%  i-  5  20% 

8c.p.lamp=      5%  1-2^  40% 

Stopped        =      2%  i-  i  100% 

In  order  to  avoid  such  a  poor  showing  as  the  above,  a 
friction  compensator  is  introduced  which,  theoretically,  com- 
pensates for  the  friction  and  enables  the  meter  to  run 
correctly  under  all  loads.  Since  this  friction  compensator 
is  not  automatic  in  its  operation,  that  is,  does  not  increase 
as  the  friction  increases,  it  affords  only  imperfect  relief, 
as  the  increasing  of  the  frictional  torque  by  ten  would  stop 
the  meter  on  20  per  cent,  of  its  full  load. 

The  remedy  lies  in  increasing  the  ratio.  If  the  friction 
remain  the  same,  the  doubling  of  the  torque  in  the  fore- 
going table  would  result  in  the  following: 


TORQUE  AND  FRICTION. 


Load. 


Full 

Half  . . . 
Quarter. 

20%.... 
10% 


2% 


Friction-Torque. 
I-IOO 
I-  50 
I-  25 
I-  20 
I-  10 

J-     5 

I-       2 


Increasing  the  friction  by  ten  in  this  instance  would  stop 
the  meter  on  ten  per  cent,  of  its  load,  and  make  it  ten  per 
cent,  slow  on  full  load  instead  of  20  per  cent,  slow  on  full 
load  as  under  the  conditions  assumed  for  the  previous 
table. 

Carrying  out  this  principle  one  could  get  a  meter  that 
for  all  commercial  considerations  would  be  correct  through 
all  ranges  of  load.  Two  things  must  be  done  to  accomplish 
this  result,  namely,  increase  the  torque  and  reduce  the 
friction.  The  most  economic  course  is  to  eliminate  friction, 
as  this  keeps  down  the  power  consumption  of  the  meter. 
When  the  frictional  equivalent  is  reduced  to  its  minimum 
for  a  given  form  of  construction,  the  friction -torque  ratio 
at  full  load  for  any  meter  should  not  be  less  than  1 1400. 
This  ratio  with  no  friction  compensator  gives  a  two  and 
one-half  per  cent,  error  on  ten  per  cent,  of  full  load,  which 
is  close  enough  for  commercial  use;  it  would  mean  an 
error  of  1.2  watts  with  one  light  burning  on  a  five  ampere 
meter. 

It  is  evident  from  the  foregoing  that  there  is  an  economic 
limit  to  the  increase  of  the  torque  of  a  meter  to  obtain 
greater  accuracy.  When  this  increase  in  torque  is  directly 
proportional  to  the  increase  in  current  necessary  to  produce 
it,  it  is  possible  to  consume  more  power  in  obtaining 


50  AMERICAN  METER  PRACTICE. 

extreme  accuracy  than  the  amount  of  power  lost  through 
inaccuracy.  If  the  ratio  1 1400  were  doubled,  making  it 
i  :8oo,  and  this  entailed  increasing  the  power  consumption 
of  the  meter  by  three  watts,  nothing  would  be  gained;  on 
the  contrary,  a  loss  would  be  sustained  of  1.8  watts  on  any 
load  the  meter  registered. 

By  assuming  a  fixed  frictional  equivalent,  the  economical 
torque  of  any  meter  can  be  worked  out.  In  all  forms  of 
motor  meters  the  design  should  be  such  that  the  maximum 
torque  should  be  obtained  for  a  given  input  in  current. 
If  all  meter  losses  in  a  given  case  amount  to  five  watts^. 
the  meter  should  have  a  resultant  torque  approaching  as 
closely  as  possible  its  mechanical  equivalent,  or  about  t|» 
horse-power.  As  a  rule  meters  are  very  inefficient,  con- 
sidered as  motors,  and  cannot  be  otherwise  from  their  con- 
struction. 

In  a  5oo-wattmeter,  assume  that  the  friction  has  been 
reduced  to  its  lowest  possible  limit,  and  that  the  meter 
consumes  at  full  load  six  watts  in  its  shunt  and  field  coils. 
With  this  consumption  of  energy,  also  assume  the  friction- 
torque  ratio  to  be  1:100.  The  meter,  if  uncompensated, 
would  lose  one  per  cent.,  or  five  watts,  at  full  load  from 
friction.  If  eight  watts  were  consumed  by  the  meter  and 
the  torque  thereby  increased  by  33^-  per  cent.,  the  friction- 
torque  ratio  would  be  1:133^,  and  the  error  at  full  load 
three  and  three-fourths  watts.  If  nine  watts  were  con- 
sumed by  the  meter  and  the  torque  thereby  increased  by 
50  per  cent.,  the  friction-torque  ratio  would  be  1:150,  and 
the  error  at  full  load  would  be  three  and  one-third  watts. 
The  net  gain,  therefore,  would  be  only  one-third  watt,  so 
this  ratio  of  1 1150  could  be  assumed  to  be  about  the  point 
of  economical  balance,  beyond  which  there  would  be  no 
gain  in  further  increasing  the  torque  at  the  expense  of 


TORQUE  AND  FRICTION.  51 

further  loss  of  power.  Where  the  friction  is  an  absolute 
fixed  quantity,  the  friction-torque  ratio  of  any  given  meter 
may  be  worked  out  in  the  same  way. 

A  graphic  method  of  determining  the  friction-torque 
ratio  of  a  given  meter  is  as  follows:  Adjust  the  friction 
compensator  on  no  load  so  that  the  meter  is  just  balanced ;; 
that  is,  so  that  it  will  creep  under  the  slightest  vibra- 
tion. When  this  is  done,  turn  on  the  full  capacity  of 
the  meter  and  take  its  speed  under  full  load;  then 
remove  the  friction  compensator  and  note  the  difference 
in  the  speed  of  the  meter  under  the  same  load.  The  per- 
centage of  slowness  will  be  inversely  proportional  to  the 
friction-torque  ratio;  thus,  two  per  cent,  would  mean 
1 150 ;  one  per  cent.,  i  :ioo;  and  so  on.  When  the  friction- 
torque  ratio  is  determined,  it  is  very  easy  to  figure  out  the 
gain  or  loss  that  the  consumption  of  additional  power  to 
increase  the  torque  would  entail. 

Meters  with  ratios  under  1 1400  are  the  rule  rather  than 
the  exception,  but  their  frictional  equivalent  is  such  that 
it  is  impossible  to  better  them.  '  Many  meters  fail  in  com- 
mercial service  by  having  an  unstable  frictional  equivalent, 
through  faulty  mechanical  design  or  improper  protection 
of  the  revolving  parts  from  foreign  matter. 

The  correct  end  of  all  meter  design  is  towards  an  un- 
changing frictional  equivalent  of  infinitesimal  amount  and 
the  largest  possible  economic  torque  determined  by  the 
rules  laid  down  above.  Friction  compensators  should  be 
discarded  where  possible. 

Meters  vary  in  the  amount  of  power  required  in  their 
potential  circuits,  and,  also,  in  the  amount  used  in  the  field 
windings.  The  values  of  these  combined  amounts  should 
be  taken  at  full  load  of  the  meter  and  a  tabulated  set  of 
friction-torque  ratios  put  down.  The  ratio  for  a  given  loss 


52  AMERICAN  METER  PRACTICE. 

of  power  can  be  found  by  ascertaining  the  loss  in  registra- 
tion at  full  load  of  the  meter  caused  by  the  friction,  and 
compensating  for  this  by  giving  the  meter  more  torque  at 
an  increased  expenditure  of  energy.  From  the  tabulated 
values  it  is  a  simple  matter  to  select  a  friction-torque  ratio 
that  cannot  be  increased  unless  more  energy  is  expended 
than  will  be  saved  by  the  increased  accuracy  obtained. 

In  the  following  tables  three  different  amounts  of  power 
loss  are  assumed  in  relation  with  the  same  friction-torque 
ratios;  the  balancing  ratios  obtained  represent  the  correct 
design  of  the  meter  to  obtain  the  highest  economy  under 
any  one  of  the  given  conditions. 

TABLE  I 

Consumption  in  Watts  Correct  Watts  True 

Ratio  in  Meter  at  Full  Load.  for  Balancing  Ratio.     Balancing  Ratio. 

1-50  2  5  -   125  app. 

i-   100  2  4  -  200 

I-  200  2  3H  -  325 

I-  400  2  2%  -  550 

I-  800  2  2^  -1000 

i-iooo  The  highest  economic  balance  at  2^  watts  consumption  of 
current. 

TABLE  II 

-  50                       4                                        8  i-ioo  app. 

-zoo                       4                                        6  1-150 

-200                       4                                        5^  1-275 

-400                       4                                        5  1-500 

-500  The  highest  economic  balance  at  5  watts  consumption  of 
current. 

TABLE  III 

1-50  6  ii  i-  90  app. 

i-ioo  6  9  1-150 

1-200  6  7%  1-250 

1-250  Approximate  highest  economic  balance  at  7%  watts  con- 
sumption of  current. 


TORQUE  AND  FRICTION.  53 

These  tables  show  that  for  different  values  of  the  fric- 
tional  equivalent  the  amount  of  energy  necessary  to  pro- 
duce the  best  results  varies  accordingly.  For  example, 
in  Table  I  the  ratio  1-50  with  2  watts  consumption  of 
current  is  an  inefficient  ratio;  the  true  ratio  should  be 
1:125  with  5  watts  consumption  of  current. 

In  Table  II  the  ratio  1-50  shows  that  it  should  be  i-ioo 
with  8  watts  consumed  instead  of  4.  As  the  energy  torque 
remains  the  same  and  the  friction  decreases,  a  ratio  is 
reached  wherein  no  change  either  way  can  be  made  to 
make  the  meter  more  efficient.  In  Table  I  this  ratio  is 
i- 1 ooo  with  i\  watts  consumption  of  energy. 

As  the  consumption  of  energy  increases,  as  shown  in 
Tables  II  and  III,  the  ratios  diminish  in  direct  proportion. 
If  a  ratio  of  1-50  consume  10  watts,  it  is  balanced,  and  the 
meter  cannot  be  improved  by  increasing  the  watt  con- 
sumption. 

Tables  can  be  made  of  various  watt  losses  of  different 
meters,  and  economic  balance  of  any  meter  obtained  after 
its  ratio  is  found. 

The  foregoing  tables  will  be  useful  for  designers  and  also 
to  the  central  station  in  the  selection  of  meters.  It  is 
assumed  in  the  foregoing  that  the  frictional  equivalent  is 
uncompensated,  but,  as  the  majority  of  manufacturers  try 
to  compensate  the  frictional  losses  of  their  meters,  the  ratio 
of  almost  all  meters  on  the  market  can  be  obtained  as  out- 
lined without  much  difficulty. 

The  Stanley  meter  is  uncompensated,  the  frictional  equiv- 
alent being  so  slight  that  it  has  a  very  large  ratio.  The 
ratio  can  be  determined  on  this  meter  by  noting  the  num- 
ber of  watts  on  which  it  starts.  This  per  cent,  of  the  full 
load  capacity  would  determine  the  ratio  of  the  meter  with 
reasonable  accuracy. 


54  AMERICAN  METER  PRACTICE. 

Too  much  stress  connot  be  laid  on  low  and  permanent 
frictional  equivalent.  If  these  elements  can  be  fixed  it  is  an 
easy  matter  to  build  an  accurate  meter  for  all  loads. 

It  is  customary  among  meter  manufacturers  to  maintain 
the  torque  for  the  same  percentage  of  load  constant  through 
various  sizes  of  meters.  Thus  a  five  ampere  meter  may  run 
at  the  rate  of  one  revolution  in  four  seconds  on  full  load, 
and  a  100  ampere  meter  run  at  the  same  rate  on  full  load. 

The  registration  on  the  dials  is  corrected  either  by  multi- 
plying by  a  constant  or  changing  the  ratio  between  the 
revolving  armature  and  the  registering  train. 

A  100  ampere  meter,  therefore,  with  a  ratio  of  1—50 
would  have  a  ratio  of  i  to  5  on  20  lights  or  20  per  cent, 
.-slow  on  this  load  on  two  per  cent,  of  its  capacity  it  would 
•stop,  that  is,  on  four  lights.  Of  course,  the  friction  is 
compensated  for  as  far  as  possible,  but  any  increase  in 
friction  makes  the  above  conditions  more  aggravated. 

Any  meter  therefore  with  such  a  ratio  is  absolutely  un- 
reliable and  can  never  be  made  to  run  correctly.  The 
central  station  is  the  loser. 

A  different  set  of  tables  must,  therefore,  be  made  up  for 
each  capacity  of  meter,  and  its  balancing  ratio  obtained  to 
determine  just  where  it  stands  with  regard  to  accuracy. 

If  a  100  ampere  meter  with  a  ratio  of  1-50  be  installed 
and  the  friction  compensated  for,  it  may  run  approxi- 
mately correct  for  a  short  period,  but  the  friction  is  liable 
,to  treble  or  quadruple  itself  at  any  time,  and  the  com- 
jpensator  will  only  take  care  of  the  original  friction  value. 

A  curve  of  the  meter's  running  can  be  plotted  showing 
the  per  cent,  slow  at  various  increases  in  friction. 

If  we  take  a  meter  of  500  watts  capacity  as  a  base  from 
which  to  deduct  different  values  for  friction  and  torque, 
we  .arrive  at  ratios  given  in  the  following  tables. 


TORQUE  AND  FRICTION. 

We  will  suppose  that,  if  a  certain  torque  be  obtained  b 
given  input  in  watts  in  the  meter,  a  larger  or  smaller 
input  will  increase  or  decrease  the  torque  in  direct  pro- 
portion. 

If  the  meter  have  no  compensation  for  its  friction,  it  will 
run  at  various  percentages  slow  according  to  the  load; 
thus  a  meter  two  per  cent,  slow  on  full  load  will  be  four 
per  cent,  on  half  load  and  so  on. 


TABLE  I 


Watt  Loss 
in 


Watt  Loss    Total  Losses 
due  in  Meter  and 


Friction. 

Torque  . 

Meter. 

Ratio. 

to  Friction. 

by  Friction 

%  Slow. 

•05 

50 

IO 

I—  IOOO 

1A 

10^ 

I-IO  Of   I< 

.  I 

5° 

IO 

I-  500 

i 

II 

i/5  of  i  < 

.  2 

5° 

IO 

I—  250 

2 

12 

2/5  of  i< 

-4 

50 

IO 

I-  125 

4 

14 

4/5  of  i  < 

i 

5° 

10 

I-    50 

IO 

2O 

2% 

2 

5° 

10 

I-     25 

20 

30 

4% 

4 

5° 

10 

i-     12^; 

2           40 

5° 

8% 

5 

5° 

10 

I-        10 

50 

60 

10% 

10 

5° 

10 

I-       5 

IOO 

no 

20% 

25 

5° 

10 

I-           2 

250 

260 

50% 

.50 

5° 

IO 

I-           I 

500 

5io 

stopped. 

TABLE  II      (Doubling  the  Torque  by  Doubling  Input.) 

2O*4        I/2O  Of   I  ' 

i/io  of  i; 
i/5  of  i; 
2/5  ofi; 


2% 

4% 


.05 

IOO 

20 

I-20OO 

M 

20 

.  I 

IOO 

20 

I—  IOOO 

Vz 

20 

.2 

IOO 

20 

I-  5OO 

I 

21 

•4 

IOO 

20 

I-  250 

2 

22 

J 

IOO 

2O 

I-  IOO 

5 

25 

2 

IOO 

2O 

I-  50 

IO 

3° 

4 

IOO 

20 

I-  25 

20 

40 

5 

IOO 

2O 

I-  20 

25 

45 

IO 

IOO 

2O 

I-   10 

50 

70 

25 

IOO 

20 

I-    4 

I25 

145 

5° 

IOO 

20 

I—    2 

250 

270 

50% 


56 


AMERICAN  METER  PRACTICE. 


TABLE  III 


Watt  Loss 
in 


Watt  Loss 

due         Total  Losses 


Friction. 

Torque. 

Meter. 

Ratio. 

to  Friction. 

in  Meter 

.001 

10 

2 

-400 

JM 

3/4 

•05 

IO 

2 

—  2OO 

2^ 

4^ 

.1 

10 

2 

-IOO 

5 

7 

I 

.2 

IO 

2 

-  5° 

IO 

12 

2 

•4 

10 

2 

~    25 

20 

22 

4 

i 

IO 

2 

-    10 

50 

52 

10 

2 

10 

2 

-     5 

IOO 

IO2 

20 

4 

10 

2 

-       2^ 

200 

2O2 

40 

5 

IO 

2 

—       2 

250 

252 

50 

10 

10 

2 

-       I 

500 

502 

stc 

%  Slov 


TABLE  IV 


.001 

20 

4 

[-800 

.  62  J 

^      4.62 

H      Hof 

i% 

.05 

2O 

4 

—400 

I  ^^ 

sM 

&of 

i% 

.1 

20 

4 

—200 

2^ 

6^ 

Hof 

i% 

.  2 

2O 

4 

-IOO 

5 

9 

1% 

•  4 

20 

4 

-  50 

IO 

14 

2% 

i 

20 

4 

-    20 

25 

29 

5% 

2 

20 

4 

—    IO 

50 

54 

io9o 

4 

20 

4' 

-     5 

IOO 

104 

20% 

5 

20 

4 

-     4 

125 

129 

25% 

IO 

20 

4 

—       2 

250 

254 

50% 

20 

2O 

4            3 

—        I 

500 

5°4 

stopped 

In  the  Tables  I,  II,  III  and  IV  we  have  meters  con- 
suming 2,  4,  10,  20  watts  respectively.  These  meters  are 
supposed  to  operate  at  the  same  efficiency  per  watt,  that 
is,  have  the  same  torque  per  watt. 

Various  friction  values  are  assumed,  the  unit  of  friction 
being  taken  as  some  proportion  of  the  torque  unit. 

In  Table  I  a  meter  having  a  friction  value  of  .05  and 
torque  value  of  50  with  a  watt  consumption  of  10  has  a 
ratio  of  i-iooo,  and  the  total  meter  losses  are  loj  watts. 


TORQUE  AND  FRICTION.  57 

The  same  meter,  Table  II,  with  double  the  torque  and 
double  the  watt  input  has  a  ratio  of  1-2000  and  total 
meter  losses  on  full  load  of  20 J  watts. 

It  is  seen  at  a  glance  that  the  lower  torque  meter  Table 
i  is  the  more  efficient. 

In  Table  III  a  low  torque  meter  having  the  same  frictional 
value  with  2  watts  input  has  total  watt  losses  on  full  load 
of  4*. 

These  tables  enable  one  to  ascertain  the  correct  watt 
input  of  a  meter  having  a  given  frictional  equivalent  for 
the  most  economical  running. 

In  these  tables  the  watt  losses  at  full  load  are  given  for 
various  friction  values,  *and  it  is  seen  that  the  low  torque 
meters  are  the  most  economical  on  low  friction  values  and 
the  high  torque  meters  on  large  friction  values.  In  other 
words,  every  meter  having  a  given  frictional  equivalent 
has  a  balancing  ratio  at  which  it  will  operate  most 
economically  and  correctly. 

Table  I  from  .05  to  .2  frictional  equivalents,  we  find  by 
comparison  that  Table  III  is  far  more  economical,  while  for 
values  from  .2  to  10,  Table  I  is  the  best. 

Like  comparison  can  be  made  for  various  values  in  the 
different  tables. 

These  tables  are  calculated  for  the  purpose  of  showing 
the  losses  due  to  uncompensated  friction.  As  nearly  all 
meters  are  compensated,  these  tables  do  not  apply  when 
the  meter  is  correct,  but  should  the  friction  equivalent 
become  increased  while  in  service,  the  losses  set  forth 
would  occur. 

The  lines  to  be  pursued  in  obtaining  a  correct  meter  are 
the  reducing  of  the  frictional  equivalent  to  its  lowest 
permanent  value  and  the  designing  of  the  meter  electrically 
for  its  greatest  efficiency  per  watt  input. 


58  AMERICAN  METER  PRACTICE. 

In  other  words,  if  a  meter  consume  four  watts  on  full 
load  and  have  a  torque  value  of  20,  the  frictional  equivalent 
must  be  at  least  as  low  as  .4  of  this  amount,  or  it  becomes 
more  economical  to  consume  more  than  4  watts  to  obtain 
a  larger  torque.  The  ratio  must  not  fall  below  1-50. 
If  a  ratio  between  torque  and  friction  of  i-ioo  be 
obtained,  the  wattage  can  be  reduced  to  2  with  more 
economical  results  as  shown  (Table  III). 

With  high  friction  values  we  get  better  results  by  using 
more  watt  input.  For  instance,  with  a  ratio  i-io  (Table 
III)  we  get  52  watts  loss;  the  same  friction  value  (Table  IV) 
gives  us  a  ratio  1-20,  watt  loss  29,  while  in  Table  i  we 
have  a  ratio  1-50,  watt  loss  20.  The  same  friction  value, 
Table  II,  gives  a  ratio  i-ioo,  watt  loss  25,  showing  that 
ratio  1-50,  watt  loss  20,  is  the  balancing  ratio. 

In  the  foregoing  it  is  assumed  that  the  central  station, 
not  the  consumer,  pays  for  the  loss  in  the  meters. 


CHAPTER  V. 
The  Edison  Chemical  Meter. 

Almost  from  the  inception  of  electric  lighting  the  Edison 
chemical  meter  has  been  used  for  the  metering  of  direct 
currents.  In  theory  it  is  an  ampere  hour  meter,  and  with 
proper  manipulation  and  care  it  proves  a  wonderfully 
accurate  meter  in  service. 

If  two  plates  of  zinc  be  immersed  in  a  solution  of  sul- 
phate of  zinc  and  a  current  passed  from  one  plate  to  the 
other  through  the  solution,  zinc  is  carried  over  from  the 


FIG.   18 

positive  plate  and  deposited  on  the  negative  in  direct  pro- 
portion to  the  amount  of  current  flowing.  This  principle  is 
utilized  in  the  Edison  chemical  meter. 

In  a  solution  of  zinc  sulphate  having  a  density  i.n,  one 
ampere  of  current  will  deposit  1.224  grams  of  zinc  per  hour. 
This  rate  of  deposit  would  necessitate  liaving  plates  weigh- 
ing a  ton  to  register  large  amounts  of  current.  This  diffi- 
culty is  surmounted  by  using  a  shunt  of  low  resistance  and 
allowing  only  a  small  fraction  of  the  current  to  be  used  in 
registering,  the  amperes  flowing  in  the  circuit.  Fig.  18 

59 


60 


AMERICAN  METER  PRACTICE. 


represents,  diagrammatically,  the  arrangement  of  the  meter 
for  the  two-wire  system.  It  is  observed  that  there  are  two 
bottles  each  containing  two  plates  held  at  a  fixed  distance 
from  each  other  by  rubber  bolts  and  spacers.  Two  bottles 
instead  ot  one  are  used  to  serve  as  a  check  on  each  other. 
A  is  the  low  resistance  German  silver  shunt,  B  and 
C  are  spools  on  which  is  wound  copper  wire  of  com- 
paratively high  resistance.  In  the  12  light  meter  the  shunt 
has  approximately  .02  ohm  resistance  and  the  bottle  cir- 
cuit 19.50  ohms,  of  which  the  spool  has  about  16.50  ohms 
and  the  bottle  3  ohms,  making  a  relation  of  i  to  975  be- 


fWWVWWWWW* 


FIG.  19. 

tween  the  shunt  and  bottle.  From  this  relation  a  constant 
is  worked  out  for  the  meter  to  determine  the  amount  of 
money  one  grain  or  fraction  thereof  represents.  This  con- 
stant varies  with  the  voltage  of  the  circuit  employed  if  the 
service  be  charged  for  by  watt-hours. 

In  the  three-wire  meter,  Fig.  19,  a  shunt  is  inserted  in 
each  outside  leg,  making  simply  two  two-wire  meters  under 
the  same  cover.  The  meter  is  made  in  a  number  of  com- 
mercial sizes,  and  these  can  be  made  of  longer  recording 
capacity  by  increasing  the  resistance  of  the  bottle  circuit. 


EDISON  CHEMICAL  METER.  61 

The  zinc  plates  are  mounted  on  hard  copper  rods  threaded 
into  the  top  end.  The  glass  bottles  resemble  fruit  jars 
with  two  holes  in  the  cover  for  the  extended  rods.  Of  late 
years  a  large  cork  was  used  instead  of  the  glass  top  and 
considerable  time  saved  in  assembling  the  cells.  The 
whole  meter  was  mounted  in  a  well  seasoned  wooden  box 
having  a  sheet  iron  door  with  a  shelf  provided  midway  in 
the  meter  for  the  reception  of  the  bottles.  The  low  re- 
sistance shunts  were  contained  in  the  lower  part  of  the 
meter.  The  hard  copper  rods  were  pushed  into  hard 
copper  spring  contact  clips  for  connecting  them  in  circuit. 
In  cold  climates  a  lamp  in  series  with  a  thermostat  is 
placed  in  the  meter  compartment  for  furnishing  heat  if  the 
temperature  falls  near  freezing  point.  The  temperature 
coefficient  of  the  meter  is  preserved  at  unity  by  winding 
the  resistance  spools  with  copper  wire,  as  copper  increases 
in  resistance  and  German  silver  decreases  as  they  grow 
warmer.  The  solution  decreases  in  resistance  as  it  grows 
warmer,  so  the  copper  spools  become  a  balancing  factor 
between  the  German  silver  shunt  and  the  solution.  The 
fall  of  potential  across  the  shunts  is  so  slight  as  to  make  the 
energy  losses  of  the  meter  inappreciable ;  the  nature  of  the 
loss  being  the  same  as  a  line  loss,  and  not  a  consumption  of 
additional  energy. 

By  following  the  meter  through  its  practical  operation 
in  the  meter  department  its  different  features  will  be 
clearly  brought  out.  The  zinc  plates  must  be  chemically 
pure,  or,  otherwise,  battery  action  will  be  set  up  in  the  cell 
and  a  counter  electromotive  force  generated  which  will 
destroy  the  accuracy  of  the  register. 

When  the  plates  are  received  from  the  makers  they  are 
rough  stampings  with  the  hard  copper  rods  screwed  into 
.their  ends.  The  first  operation  is  to  polish  them  smoothly 


62  AMERICAN  METER  PRACTICE. 

on  a  sand  wheel  and  then  amalgamate  them  in  mercury. 
The  surplus  mercury  is  removed  by  a  revolving  brush.  The 
finished  plate  is  smooth  and  silvery  in  appearance.  The 
mercury  has  the  effect  of  rendering  the  plate  active  and 
eats  its  way  inward  as  the  zinc  is  deposited  from  one  plate 
to  the  other.  The  bare  zinc  plate  unmalgamated  seems 
to  possess  a  sort  of  resisting  property  to  free  action  which 
hinders  it  from  being  deposited  at  a  uniform  rate.  The 
joint  between  the  zinc  plate  and  copper  rod  should  be 
painted  with  black  asphaltum  paint  to  keep  the  mercury 
from  eating  away  the  copper  and  allowing  the  rod  to  be- 
come loose  in  the  joint.  This  paint  is  put  on  before  the 
plate  is  amalgamated.  When  ready  to  be  ^eighed  it  is  tested 
across  the  joint  with  a  galvanometer  to  insure  the  presence 
of  a  perfect  electrical  joint.  It  is  found  that,  after  the 
plates  have  been  in  service  for  some  time,  this  joint  fre- 
quently becomes  defective,  and  a  resistance  is  thereby  added 
to  the  bottle  circuit  which  makes  the  meter  register  less 
than  it  should.  Analytical  balances  of  the  greatest  del- 
icacy are  used  in  weighing  the  plates  and  the  plates  are 
weighed  to  within  5  milligrams.  Two  methods  of  weigh- 
ing are  in  use;  the  single  and  double  system.  As  only 
one  plate  loses  weight,  the  positive  one,  the  single  method 
of  weighing  records  its  weight  on  suitable  slips,  and  when 
the  plate  comes  back  at  the  end  of  the  month  its  lost  weight 
is  proportional  to  the  amount  of  current  used.  If  the  plate 
be  reversed  in  the  meter,  the  weighed  plate  gains  in  weight 
instead  of  losing.  The  gain  or  loss  represents  the  amount 
of  current  used.  The  double  weighing  system  weighs  both 
positive  and  negative  plates  on  a  double  rider  balance,  the 
net  difference  in  weight  being  recorded.  When  the  plates 
are  returned  the  net  difference  is  again  noted  and  the  loss 
recorded  on  the  slip. 


EDISON  CHEMICAL  METER.  63 

After  the  plates  are  weighed  by  one  operator  they  should 
be  check  weighed  to  eliminate  errors  by  another  operator. 
Each  plate  is  given  a  number  and  letter  written  on  the  back 
of  the  plate  itself,  so  as  to  identify  it  on  its  return  to  the 
meter  department.  From  the  weighing  bench  the  plates 
are  taken  to  be  assembled,  which  consists  of  bolting 
positive  and  negative  together,  and  separating  them 
by  insulating  spacers  of  a  fixed  width.  The  plates 
are  reground  and  used  over  and  over  again  until  they 
wear  out.  The  preparation  of  the  solution  must  be  care- 
fully done,  and  all  the  ingredients  must  be  chemically  pure. 
Distilled  water  and  sulphate  of  zinc  are  the  two  ingredients, 
and  these  are  mixed  in  solution  to  a  density  of  i.n  actual. 
After  mixing,  the  solution  is  filtered  to  remove  any  foreign 
particles  that  may  have  fallen  into  it.  The  bottles  are 
washed  clean,  and  the  assembled  plates  put  in  with  the 
solution  covering  them  for  about  half  an  inch.  When  a 
large  number  of  bottles  are  handled  daily,  special  tanks  of 
porcelain  or  glass  should  be  arranged  to  hold  the  solution, 
and  the  bottles  filled  from  them  by  a  flexible  hose  with 
faucet  attached. 

A  given  number  of  meters  should  be  read  each  day,  and 
they  should  be  listed  according  to  location  and  a  route 
list  given  to  the  man  changing  the  bottles. 

The  great  secret  of  success  in  the  metering  of  current  in 
this  way  lies  in  the  exercise  of  extreme  care  in  each 
operation.  Carelessness  in  any  one  part  of  the  work 
affects  the  whole  system.  In  the  installation  of  the  bottles 
in  the  meter  care  must  be  taken  to  place  the  positive  plate 
to  the  positive  clip  of  the  meter,  otherwise  reversed  plates 
will  be  the  result.  It  is  the  practice  in  some  plants  to  put 
one  bottle  in  reversed  and  one  bottle  the  right  way  and  take 
the  average  of  the  sum  of  the  readings,  but  this  method  is 


64  AMERICAN  METER  PRACTICE. 

open  to  objection  if  the  bottles  become  "smutted"  from 
excessive  load. 

The  "smutting"  of  the  plates  is  caused  by  the  too  rapid 
deposition  of  the  zinc,  and,  if  carried  on  too  long,  the  plates 
are  bridged  across  with  black  bridges  resembling  coke. 
This  short  circuiting  of  the  plates  shunts  them,  and  makes 
them  register  less  than  they  should.  When  a  meter  is 
found  to  smut  badly,  even  if  it  do  not  short  circuit,  the 
bottles  should  be  renewed  oftener  or  a  larger  meter  put 
in.  It  has  been  found,  by  a  careful  series  of  tests  by  the 
author,  that  a  heavy  smutting  increases  the  registration 
by  about  10  per  cent.,  and  a  short  circuit  decreases  the 
registration  by  a  varying  quantity  dependent  on  how  many 
bridges  have  been  built  up  between  the  two  plates.  It 
was  found  that,  where  there  was  excessive  vibration, 
the  bottles  gradually  crept  out  of  the  clips  and  ceased  to 
register.  Again,  it  was  found  that  verdigris  and  dirt  fre- 
quently introduced  a  resistance  in  circuit  which  kept  the 
meters  from  registering  all  that  they  should.  Consider- 
ations of  this  nature  led  to  the  adoption  of  a  cast  brass 
clip  in  which  holes  were  provided  for  the  reception  of  the 
copper  rod  terminals  of  the  cells.  A  set  screw  was  pro- 
vided for  setting  the  rods  up  hard  in  the  hole,  and  it  was 
impossible  to  get  them  loose.  The  grinding  movement  of 
the  screw  on  the  rod  insured  a  good  contact.  The  great 
improvement  in  the  registration  of  the  meters  led  to  their 
adoption  for  the  entire  system  of  a  large  plant.  It  was  the 
watching  of  every  minute  detail  and  the  careful  handling 
of  this  meter  that  made  it  a  commercial  possibility  for 
20  years. 

The  great  drawback  to  the  meter  is  that  it  cannot  be 
read  by  the  consumer.  The  consumer  was,  so  he  thought, 
absolutely  at  the  mercy  of  the  company  furnishing  current, 


^  OFTHE 

,    UNIVERSITY   ) 

Of 


EDISON  CHEMICAL  METER.  65 

and  he  could  seldom  follow  the  process  of  measuring  the 
current  intelligently  when  the  method  was  explained  to 
him.  Another  great  drawback  to  the  meter  is  that  it  has 
no  rate  of  measurement  from  which  to  determine  its  ac- 
curacy. In  other  words,  if  a  reading  failed  for  one  month 
owing  to  some  accident,  the  only  recourse  was  to  take  a 
check  reading  and  estimate  the  bill.  In  a  mechanical 
meter,  if  the  reading  be  disputed,  a  test  can  be  made  of 
the  meter  and  a  determination  made  of  its  accuracy,  from 
which  a  bill  can  be  checked  up  with  a  fair  amount  of  pre- 
cision. On  the  other  hand,  the  chemical  meter  could  not 
"run  slow"  for  more  than  a  month,  as  it  was  practically  a 
new  meter  after  each  renewal. 

After  the  bottles  have  stood  for  a  month,  even  if  no  cur- 
rent be  used,  a  slight  oxidation  takes  place  which  increases 
the  weight  of  the  plate  slightly. 

When  the  bottles  are  taken  apart,  if  the  single  plate 
method  of  weighing  be  used,  the  plates  are  dipped  for  a 
moment  in  dilute  sulphuric  acid  and  quickly  rinsed.  This 
removes  the  slight  over-weight  caused  by  oxidation.  When 
the  double  plate  method  of  weighing  is  used,  the  oxidation 
on  the  negative  and  positive  plates  cancel  each  other,  so  no 
dipping  is  required. 

The  relation  between  the  shunt  and  bottle  circuits 
rarely  changes,  and  when  it  does  it  is  nearly  always 
due  to  an  open  circuit  in  the  spool.  The  infinitesimal 
difference  of  potential  between  the  adjacent  coils  in 
the  spools  renders  a  short  circuit  in  them  practically  out 
of  the  question.  However,  the  precaution  is  taken  to  boil 
the  spools  in  paraffine. 

The  labor  of  maintaining  the  meters  is  excessive,  and 
the  details,  when  a  large  number  of  meters  are  operated, 
cumbersome. 


66  AMERICAN  METER  PRACTICE. 

The  chemical  meter  is  passing  out  of  use.  Its  com- 
mercial accuracy  is  equal  to  many  mechanical  meters,  but 
there  are  advantages  in  the  mechanical  type  which  offset 
some  of  the  advantages  which  the  chemical  meters  possess 
over  them. 

If  this  description  of  the  chemical  meter  were  likely  to 
prove  other  than  of  historical  interest,  many  interesting 
details  of  operation  and  arrangement  of  the  meter  depart- 
ment would  be  gone  into,  in  the  belief  that  they  might  prove 
of  service.  The  meter  has  been  barely  sketched  for  the 
purpose  of  illustrating  a  type  which  so  long  held  first  place 
in  the  meter  world,  but  which  has  passed  its  day  of  useful- 
ness. Some  of  the  requisites  of  a  good  meter  are  fulfilled 
in  this  meter.  Its  light  load  accuracy  is  very  good  on 
small  sizes  of  meters,  but  not  on  large  sizes,  owing  to  the 
modifying  effects  of  increased  oxidation  due  to  large  plates. 

Vibration  does  not  alter  the  accuracy  of  the  meter  if  the 
copper  rods  be  held  firmly  in  contact  by  set  screws.  As 
the  meter's  accuracy  is  altogether  dependent  on  the  con- 
tinued care  and  accuracy  of  many  operations,  individual 
inaccuracies  are  not  as  likely  to  occur  as  for  a  whole  system 
to  become  deranged  by  some  chemical  impurity  in  the 
solution  or  some  such  similar  cause. 

The  meter  is  not  adapted  to  the  measurement  of  alter- 
nating current,  but  can  measure  in  ampere  hours  any  con- 
stant voltage  direct  current  by  obtaining  the  proper 
constant  for  reduction  to  watt  hours. 


CHAPTER  VI. 
The  Thomson  Recording  Wattmeter. 

The  Thomson  recording  wattmeter  is  one  of  the  most 
widely  used  meters  in  America,  up  to  the  present  time.  Its 
extended  use  has  been  in  great  measure  due  to  its  being 
practically  the  only  meter  on  the  market  for  direct  current, 
and  to  its  further  quality  of  adaptability  to  all  forms  of 
service. 

Its  ability  to  register  either  alternating  or  direct  current, 
whether  the  former  be  inductive  or  non-inductive,  without 
change  of  calibration  makes  it  especially  suitable  to  the 
needs  of  central  stations  furnishing  different  kinds  of 
current. 

In  principle,  the  meter  is  a  modification  of  a  Siemens' 
dynamometer,  the  stationary  coils  of  which  are  energized 
by  the  current  flowing,  and  the  movable  coils  proportion- 
ately to  the  potential  of  the  circuit  in  which  the  meter  is 
inserted.  There  is  no  iron  employed  in  the  shunt  or  series 
field  coils,  the  shunt  coil  or  armature  being  wound  drum 
fashion  over  a  non-magnetic  skeleton  support  and  provided 
with  commutator  and  brushes. 

The  operation  of  the  dynamometer  then  becomes  that  of 
a  simple  motor.  The  current  flowing  energizes  the  fields 
and  the  potential  of  the  circuit,  the  shunt  field  coil  and 
armature. 

It  is  evident  that  the  torque  of  the  armature  will  be  pro>- 
portional  to  the  product  of  the  field  current  by  the  E.  M.  F. 
of  the  circuit  or  the  watts  passing  through  the  meter.  If 

67 


68  AMERICAN  METER  PRACTICE. 

the  potential  be  constant,  the  meter  may  be  used  as  a  re- 
cording ammeter,  as  the  torque  of  the  armature  then  varies 
as  the  amperes.  If  the  current  be  constant  and  the  voltage 
be  variable,  the  meter  maybe  used  as  a  recording  voltmeter. 

The  construction  of  the  meter  has  been  carefully  worked 
out  mechanically.  The  armature  spindle  is  supported  on  a 
spring  seated  removable  jewel  and  the  shaft  end  provided 
with  a  hardened  steel  removable  point,  which  may  be  re- 
newed when  the  jewel  becomes  defective  and  needs  re- 
placing. Secured  to  the  shaft  just  above  the  jewel  bear- 
ing is  a  copper  disk  revolving  between  the  poles  of  perma- 
nent magnets,  which  act  in  the  usual  manner  to  furnish  a 
brake  proportional  to  the  torque  on  the  armature. 

The  commutator  is  made  of  silver,  highly  polished,  and 
the  flexible  copper  brushes  bearing  on  it  are  silver  tipped. 
Silver  was  chosen  for  this  purpose  after  a  long  series  of 
experiments  with  other  metals,  owing  to  its  not  forming  a 
high  resistance  oxidized  film  over  its  surface  when  exposed 
to  the  air  for  extended  periods.  The  usual  worm  gear 
actuates  the  dial  train  which  records  in  watt  hours,  modified 
by  whatever  constant  the  meter  carries.  At  constant  i 
the  meter  records  a  watt  hour  for  every  revolution  of  the 
armature. 

In  two-wire  meters  the  field  coils  are  placed  one  on  each 
side  of  the  armature  and  connected  in  series ;  in  three-wire 
meters  the  same  position  is  occupied,  but  one  coil  is  con- 
nected in  each  side  of  the  circuit,  the  armature  acting  in 
common  for  both  fields.  Either  field  and  the  armature 
constitute  individual  recording  elements  which  will  act 
independently  of  the  other  field.  Hence,  any  unbalancing 
of  the  regular  three-wire  system  does  not  effect  the  ac- 
curacy of  the  meter.  If  the  voltage  on  both  sides  of  the 
system  be  the  same,  the  register  will  be  true  watts;  if 


THOMSON  RECORDING  WATTMETER.  69 

different,  the  error  will  be  proportional  to  the  difference 
existing.  As  the  same  error  exists  if  the  armature  be  fed 
from  across  the  two  outside  legs,  it  is  manifestly  no  gain  to 
feed  the  meter  in  this  way. 

In  series  with  the  armature  is  a  resistance  coil  to  regu- 
late the  flow  of  current  in  the  potential  circuit,  and  also  to 
reduce  the  fall  of  potential  between  the  armature  coils  and 
commutator  segments.  The  initial  friction  of  the  meter  is 
compensated  by  a  coil  in  series  with  the  armature  circuit; 
this  coil  is  wound  parallel  to  the  field  windings  and  placed 
inside  of  one  of  them,  it  is  immaterial  which.  The  coil  is 
so  proportioned  as  to  overcome  in  great  measure  the  friction 
of  the  moving  parts,  enabling  the  meter  "to  register  more 
accurately  on  light  loads.  The  torque  exerted  by  this 
auxiliary  coil  is  about  two  per  cent,  of  the  full  load  torque  of 
the  meter.  Care  must  be  taken  in  installing  the  meter  to 
secure  it  as  far  as  possible  from  vibration,  otherwise  the 
meter  will  creep,  unless  the  starting  coil  be  adjusted  to  suit 
the  local  conditions. 

Later  types  have  an  adjustable  starting  coil.  This  ad- 
justable starting  coil  is  wound  with  a  great  many  more 
turns  than  the  permanent  coil  used  in  older  types.  It  is 
carried  in  a  little  frame  which  is  movable  in  and  out  of  the 
field  coil  by  means  of  a  screw.  When  the  meter  is  installed, 
the  local  conditions  of  vibration  are  noted  and  the  auxiliary 
starting  coil  so  adjusted  as  just  to  balance  the  frictional 
torque  of  the  meter  in  its  present  position  without  allowing 
it  to  "creep."  Should  the  jewel  become  slightly  defective 
after  several  months'  use,  the  starting  coil  can  be  reset  to 
overcome  this  additional  friction  of  the  meter.  This 
arrangement  is  an  improvement  over  the  old  method  of 
having  a  permanent  additional  torque  imparted  to  the 
meter  no  matter  what  the  conditions  incident  to  its  location. 


70 


AMERICAN  METER  PRACTICE. 


When  the  meter  is  used  on  alternating  current  circuits,  we 
may  think  of  its  action  by  considering  the  circuit  for  an 
instant  of  time.  This  was  gone  into  fully  in  Chapter  II, 
and  need  not  be  further  elaborated,  but,  as  the  true  power 


FIG.  21. 

in  an  alternating  circuit  for  any  instant  of  time  is  the 
product  of  the  instantaneous  values  of  current  and  E.  M.  P., 
the  meter  registers  as  accurately  on  inductive  as  non- 
inductive  load. 


THOMSON  RECORDING  WATTMETER. 


71 


To  fulfil  the  demands  of  service  the  meter  is  manu- 
factured in  a  great  variety  of  sizes  and  types  of  ' '  low  effi- 
ciency" and  "high  efficiency,"  the  latter  type  succeeding 
the  former  in  general  commercial  use,  owing  to  its  greater 
accuracy  on  light  loads  and  lower  watt  consumption  in  the 
potential  circuit.  The  potential  circuit  of  the  high  effici- 
ency type  in  the  115-230  volt  commercial  sizes  for  light 
consumes  about  4  watts  of  energy,  the  230-500  volt  power 
meters  10  and  20  watts  respectively. 


FIG.  22. 

We  now  pass  to  the  general  consideration  of  the  meter 
and  the  means  of  connecting  it  for  registering  various 
forms  of  commercial  service. 

Fig.  21  may  be  taken  to  represent  the  general  interior 
appearance  of  the  various  forms. 

In  the  diagrammatic  representations,  Figs.  22  and  23  are 
shown  the  methods  of  connecting  all  meters  of  the  two- 
wire  type,  whether  for  light  or  power  purposes,  direct  or 


72 


AMERICAN  METER  PRACTICE. 


alternating  current.  The  service  feeds  on  the  left,  and  the 
disk  rotates  counter-clockwise  as  seen  from  the  top. 
The  high  efficiency  three-wire  type  is  connected  as  shown 
in  Fig.  24,  in  sizes  up  to  150  amperes.  Over  this  capacity 
the  circuit  is  metered  by  two  meters  of  the  two-wire  type. 
In  the  metering  of  polyphase  systems  by  the  Thomson 
meter  a  variety  of  connections  are  used.  The  characteristics 
of  the  circuit  govern  the  method  pursued. 


FIG.  23. 

Before  passing  to  the  measurement  of  Alternating  Poly- 
phase currents  we  wish  to  call  attention  to  a  grave  defect 
in  the  three-wire  meter,  Fig.  24,  which  may  lead  to  the  loss 
of  revenue  if  the  consumer  be  aware  of  the  conditions.  It 
is  seen  that  the  armature  circuit  is  fed  between  the  neu- 
tral and  one  outside  leg,  and  if  for  any  cause  a  fuse  blow 
on  this  side  of  the  system  before  the  meter,  the  remaining 
lamps  on  the  opposite  side  of  the  system  can  be  burned 
without  causing  the  meter  to  register.  Nor  can  this  defect 


THOMSON  RECORDING  WATTMETER.  73 

be  remedied  by  connecting  the  armature  across  the  two 
outside  legs,  as,  then,  if  either  fuse  blow,  the  meter  stops 
unless  some  lamps  are  in  circuit  on  that  side  of  the  system. 
In  that  event  the  armature  would  receive  less  than  one- 
half  its  voltage  and  the  meter  register  less  than  one-half  of 
what  it  should.  Therefore,  the  removal  of  a  fuse,  or  the 
splitting  up  of  the  main  switch  before  the  meter  into  single 
pole  switches,  could  be  used  by  designing  and  unscrupulous 
persons  to  rob  the  company  furnishing  current  of  a  large 


FIG.  24. 

amount  of  revenue.  No  doubt  the  manufacturers  of  this 
meter  are  fully  aware  of  this  defect,  but  the  central  station 
is  certainly  taking  chances  when  installing  it  of  being 
deprived  either  through  accident  or  by  intent  of  a  portion 
of  its  just  revenue.  There  are  a  number  of  simple  rem- 
edies that  can  be  applied  in  the  way  of  small  auxiliary 
devices  that  will  automatically  cut  the  armature  over  to 
the  live  side  of  the  circuit  and  preserve  the  proper  polarity 
of  the  leads  so  as  not  to  reverse  the  armature.  Some  such 


74 


AMERICAN  METER  PRACTICE. 


provisions  should  be  made  to  make  this  meter  a  safe  one, 
as  no  one  can  take  action  against  the  consumer  for 
removing  a  plug  and  burning  half  of  his  lights,  when  he  in 
no  way  touches  or  molests  the  meter. 

The  temptation  for  a  certain  class  of  customers,  when 
they  understand  the  meter,  is  too  great  for  them  not  to 


Load 


FlG.    25. 

take  advantage  of  what  is  obviously  the  fault  of  the  com- 
pany in  providing  such  a  simple  and  safe  meter  to  "beat." 
The  theory  of  the  measurement  of  polyphase  systems 
by  means  of  non-inductive  meters  has  been  set  forth  in 
Chapter  II;  hence,  simply  the  application  of  the  principle 
therein  outlined  will  be  given  in  the  diagrams  for  metering 
the  different  systems. 


THOMSON  RECORDING  WATTMETER. 


75 


In  balanced  three-phase  circuits,  one  two-wire  meter 
connected  in  either  one  of  the  three  legs  with  the  armature, 
fed  by  the  energy  voltage  of  the  circuit,  will  register  one- 
third  of  the  total  power  passing;  hence,  multiplying  by  3, 
we  obtain  the  total  energy  passing  in  the  three  legs  of  the 
circuit.  Such  a  connection  is  illustrated  diagrammatically 
in  Fig.  25,  where  the  armature  forms  part  of  one  of  the  legs 


Shunf 


FIG.  26. 

of  the  set  of  Y  connected  resistances.  The  voltage  from 
the  common  center  to  either  point  of  the  Y  is  energy 
voltage  of  the  system.  This  connection  may  be  used  for 
either  light  or  power,  but  must  always  be  used  on  a  bal- 
anced circuit  and  one  that  has  the  same  power  factor  for 
-each  phase. 

Unbalanced  three-phase  circuits  are  metered  by  placing 
two  two- wire  meters  in  two  legs  of  the  circuit  and  connect- 
ing one  end  of  the  armature  circuit  of  each  meter  to  the 


76 


AMERICAN  METER  PRACTICE. 


feeding  leg,  and  the  other  end  to  the  unmetered  leg.  This 
connection  is  illustrated  in  Fig.  26. 

In  an  unbalanced  three-phase  system  employing  four 
wires  in  its  distribution,  the  power  flowing  in  any  of  its 
three  phases  is  found  by  connecting  a  two-wire  meter  in 
that  phase,  and  feeding  the  armature  between  the  leg 
metered  and  the  fourth  wire  or  common  neutral. 

This  is  practically  what  is  done  in  the  balanced  three- 
wire  system,  the  difference  lying  in  the  extension  of  the 


FIG.  27. 

neutral  point  of  the  three  phases  to  the  distribution.  To 
meter  the  total  power  flowing  in  the  four-wire  unbalanced 
three-phase  system,  the  three  phases  must  be  metered  as 
shown  in  Fig.  27,  and  the  results  of  all  the  readings  added. 
In  the  two-phase  systems  employing  four  wires  in  the 
distribution,  two  meters  are  used  if  the  two  phases  be 
unbalanced  as  indicated  in  Fig.  28.  If  the  phases  be 
exactly  balanced,  one  meter  connected  in  one  phase  is 
sufficient,  the  total  energy  passing  being  double  its  indica- 
tion. The  connection  for  the  meter  is  shown  in  Fig.  29. 


THOMSON  RECORDING  WATTMETER. 


77 


Two-phase  systems  employing  a  common  return,  and 
distributed  by  means  of  three  wires,  are  metered  in  the 
same  manner  as  three-phase  systems. 

The  measurement  of  monocyclic  circuits  by  means  of 
Thomson  meters  has  been,  in  many  cases,  erroneously  con- 
summated. In  Fig.  30  one  meter  is  shown  connected  into  a 
monocyclic  secondary  circuit,  the  meter  being  of  the  three- 
wire  type  with  a  common  armature  for  both  fields.  Such  a 


FIG.  28. 

connection  will  not  give  the  correct  register  of  the  energy 
passing  in  the  circuit.  This  connection  has  been  in  use 
upwards  of  five  years,  but,  from  carefully  conducted  tests 
by  the  author,  it  has  proven  beyond  a  question  that  about 
33  YI  Per  cent-  of  the  current  remains  unregistered.  The 
manufacturers  have  now  ceased  to  put  out  this  meter  as 


78 


AMERICAN  METER  PRACTICE. 


correct,  and  meter  monocyclic  current  by  a  regular  three- 
phase  induction  meter,  or  by  means  of  two  Thomson  meters 
connected  in  the  same  manner  as  shown  in  Fig.  26,  for  un- 
balanced three-phase  circuits.  It  is  readily  seen,  where 
two  legs  of  an  unbalanced  three-phase  system  are  placed 
in  relation  with  the  potential  circuit  of  only  one  of  them, 
that  a  correct  registration  cannot  be  obtained.  In  Fig. 
30,  the  current  in -the  left  hand  field  for  a  portion  of  each 


TAAAAA! 

WrWl 


—       vwwvw   i 

Load 

Load 

FIG.  29. 

period  opposes  the  current  in  the  right  hand  field,  as  they 
differ  in  phase  by  120  degrees.  The  torque  exerted  on  the 
armature  is  the  product  of  the  algebraic  sum  of  the  two- 
field  currents  and  potential  circuits,  instead  of  the  arith- 
metical sum  of  the  two-field  currents  and  potential  circuit. 
Another  form  of  monocyclic  secondary  circuit  is  that 
shown  in  Fig.  31,  wherein  lights  and  motors  are  fed  from 
the  same  circuit,  the  teaser  current  being  measured  in- 
dependently of  the  light  circuit.  As  is  shown,  two  meters 


THOMSON  RECORDING  WATTMETER. 


79 


are  used  to  meter  the  total  energy  passing.  Various 
adaptations  of  this  meter  have  been  made  to  fulfil  special 
conditions,  such  as  the  measurements  of  arc  circuits  and 
storage  battery  circuits  where  the  one  meter  measures  the 
output  as  well  as  input  of  the  battery. 

The  Thomson  meter,  judged  in  the  light  of  the  requisites 
of  a  good  meter,  fails  in  several  qualifications,  and  has 
several  faults  peculiar  to  itself. 


FIG.  30. 

The  torque  of  the  meter  is  small  with  regard  to  its 
frictional  counter  torque,  having  a  ratio  of  50:1  in  a  new 
meter,  but  more  like  20:1  after  it  has  been  in  service  a  few 
months.  The  effects  of  this  are  slowness  on  light  loads  and 
consequent  loss  of  revenue. 

In  the  matter  of  friction  balancing,  we  have  seen  that  a 
coil  is  provided  which  produces  a  turning  movement  on  the 


80 


AMERICAN  METER  PRACTICE. 


armature  supposedly  equal  to  friction  of  the  moving  parts. 
As  this  friction  is  an  ever  varying  and  often  ever  increasing 
quantity,  the  friction  balancing  produced  by  the  coil  is  un- 
satisfactory. When  the  friction  is  diminished,  by  what- 
ever cause,  the  meter  will  "creep"  on  no  load,  and  lead  to 
complaint  and  distrust  on  the  part  of  the  consumer. 


FIG.  31. 

The  supporting  of  the  armature,  which  weighs,  complete, 
over  half  a  pound,  on  a  hardened  steel  point  resting  on  a 
highly  polished  jewel  surface,  furnishes  a  very  small  amount 
of  friction  while  the  jewel  and  shaft  end  retain  their  integ- 
rity, but  causes  no  end  of  trouble  the  minute  either  of  them 
becomes  rough. 


-  THE       T>* 

UNIVERSITY 

THOMSON  RECORDING  WA  TTMETE^S&^l^^ 

The  armature  is  subjected  to  vibration,  and  rapidly 
pounds  the  jewel  to  pieces.  This  causes  the  friction  of  the 
meter  to  increase  enormously  and  frequently  stops  it.  . 

The  tropical  type  of  meter  is  supposed  to  be  air-tight,  but 
it  is  not  sufficiently  so  to  exclude  acid  fumes,  insects  and 
dust,  and  all  of  these  exert  a  deleterious  effect  on  the 
accuracy  of  the  meter. 

An  apparently  trivial  defect  is  the  flaking  off  of  the 
paint  used  on  the  permanent  magnets.  This  paint  is 
magnetic,  and  will  stick  out  like  stiff  bristles  from  the  poles 
of  the  magnet  and  drag  on  the  disk,  retarding  the  meter 
appreciably  and  sometimes  stopping  it. 

The  remedy  for  this  trouble  lies  in  tinning  or  copper 
plating  the  magnets  instead  of  painting  them. 

From  a  long  series  of  records  kept  very  accurately,  it  was 
found  that  this  defect  was  a  very  serious  one  and  led  to  the 
loss  of  much  revenue. 

Stray  iron  filings  produce  a  like  effect,  and,  in  the  small 
meters  having  iron  set  screws  in  the  binding  post,  it  has  been 
found  that,  in  setting  up  the  screws  with  a  screw-driver, 
small  clippings  of  iron  have  been  dropped  on  the  disk  with 
the  above  result  of  slowing  or  stopping  the  meter. 

Where  vibration  is  present,  the  commutator  becomes 
rpugh  from  the  sparkling  of  the  brushes  and  creates  friction 
which  greatly  interferes  with  the  meter's  accuracy.  A 
piece  of  hard  linen  tape  passed  around  the  commutator 
and  under  the  brushes  will  polish  it  nicely  when  pulled 
briskly  to  and  fro.  Only  in  extreme  cases  should  crocus 
cloth  be  used,  as  it  lodges  small  silver  particles  in  between 
the  commutator  bars,  tending  to  short  circuit  them  unless 
a  strong  air  blast  is  used  to  dislodge  the  silver  dust. 

The  care  and  maintenance  of  the  meter  are  outlined  more 
fully  in  later  chapters. 


CHAPTER  VII. 


The  Duncan  Recording  Wattmeter,  for  Alternating  Current. 

The  Duncan  intergrating  wattmeter  for  alternating  cur- 
rent is,  in  its  present  state,  the  work  of  many  years  of 
development.  Attention  has  been  paid  to  the  mechanical 
requirements  of  a  good  meter  with  the  pleasing  result 

shown  in  the  accompanying  cut, 
Fig.  3  2 ,  which  shows  the  exterior 
appearance  of  the  meter.  Fig. 
33  gives  a  clear  idea  of  the 
interior  construction,  the  me- 
chanical and  electrical  details  of 
which  will  be  briefly  reviewed. 
The  meter  is  essentially  a 
rotating  field  alternating  current 
single-phase  motor  with  an  in- 
verted aluminum  cup  for  an 
armature,  and  its  fields  consist 
of  series  and  shunt  coils  placed 
at  angles  of  90  degrees. 

The  series  field  coil  of  an- 
nealed sheet  steel  laminations 
carries  the  form  wound  series 
coils  on  inwardly  projecting 

pole  pieces,  while  the  shunt  field  is  placed  inside  of  the 
armature  drum  with  its  axis  at  right  angles  to  the  axis  of  the 
series  fields.  The  shunt  field  is  also  wound  on  a  laminated 
core  v/hich  has  a  central  hole  to  allow  the  shaft  of  the 


FIG.  32. 


DUNCAN  RECORDING   WATTMETER. 


83 


revolving  armature  to  pass  through  it.  This  rotating  shaft 
carries  the  usual  gear  for  operating  the  dial  train,  and  is 
supported  at  its  lower  extremity  on  a  spring  seated  sapphire 
jewel  bearing.  The  pivoted  point  of  the  shaft  is  removable 


FIG.  33. 

in  event  of  its  becoming  injured.  Just  above  the  jewel 
bearing,  the  shaft  carries  the  retarding  disk,  which  revolves 
between  the  poles  of  two  permanent  magnets,  and  acts  as  a 
magnetic  brake,  the  power  of  which  is  proportional  to  the 
speed. 


84 


AMERICAN  METER  PRACTICE. 


The  operation  of  the  meter  is  as  follows : 

The  current  flowing  in  the  series  coils  sets  up  a  plane  of 
magnetization  at  right  angles  to  that  set  up  in  the  shunt 
field  coils,  but,  owing  to  the  self-induction  of  the  latter,  and 
the  impedance  in  series  with  it,  its  magnetization  lags  be- 
hind that  of  the  series  coil,  creating  a  shifting  or  rotating 
magnetic  field  which  actuates  the  closed  secondary  or 
armature  in  a  well-known  manner.  The  torque  produced 
varies  with  the  energy  flowing.  If  the  load  on  the  meter  be 
non-inductive,  the  magnetism  of  the  shunt  field  must  lag 
exactly  90  degrees  behind  the  E.  M.  F.  of  the  circuit. 


FIG,  34. 

Referring  to  the  diagrammatic  view  of  the  relation  of  the 
armature  with  the  series  and  shunt  coils,  Fig.  34,  we  find  at 
5,  a  secondary  coil  closed  through  the  resistance  8.  As  the 
current  in  the  shunt  field  coil  lags  less  than  90  degrees  be- 
hind the  E.  M.  F.,  the  resistance  8  is  so  adjusted  that  the 
induced  current  flowing  in  the  secondary  5,  acting  in  con- 
junction with  that  flowing  in  the  shunt  field  coil,  forms  a 
resultant  field  in  quadrature  with  the  E.  M.  F. 


DUNCAN  RECORDING  WATTMETER.  85 

The  initial  friction  of  the  moving  parts  is  compensated 
for  by  the  action  of  a  small  movable  disk  of  iron, 
surrounded  by  a  band  of  copper  shown  at  6,  Fig.  34.  This 
compensator  is  carried  on  an  arm  whose  axis  of  rotation  is 
co-incident  with  that  of  the  armature  shaft,  and  is  movable 
concentrically  to  the  armature  over  an  angle  of  about  1 20 
degrees.  The  purpose  of  the  compensator  is  to  give  an 
auxiliary  torque  to  the  armature  independently  of  the 
series  fields,  this  torque  being  so  adjusted  as  to  just  counter- 
balance the  friction  of  the  moving  parts.  When  the  axis 
of  the  compensator  makes  an  angle  with  the  axis  of  the 
shunt  field  coil,  its  magnetism  is  distorted  owing  to  the  iron 
in  the  compensator. 

Eddy  currents,  set  up  in  the  armature  by  these  lines  of 
force  cutting  it,  lag  behind  the  current  in  the  shunt  field 
coil.  The  consequent  magnetic  pole  of  the  inner  surface 
of  the  armature,  being  of  like  polarity,  repels,  while  the 
outer  pole  is  attracted  to  the  unlike  pole  set  up  by  the  eddy 
currents  generated  in  the  copper  band  of  the  compensator. 
Hence,  we  have  a  torque  proportional  to  the  angle  which 
the  axis  of  the  compensator  makes  with  the  axis  of  the 
shunt  field  coil.  If  the  compensator  is  moved  backwards 
or  clockwise  from  the  axis  of  the  shunt  field,  the  armature 
receives  a  corresponding  torque  of  reverse  direction. 

The  very  easy  manner  in  which  this  compensator  can  be 
shifted  enables  the  meter  to  be  adjusted  to  suit  a  local  con- 
dition; that  is,  if  vibration  be  present,  the  meter  may  creep 
under  the  adjustment  suitable  for  no  vibration,  but  can  be 
adjusted  to  just  balance  the  friction  on  the  customer's 
premises  without  altering  the  adjustment  on  full  load. 

This  compensator  answers  the  same  purpose  that  the 
auxiliary  coils  in  other  meters  do  with  the  advantage,  in  its 
form,  of  being  more  readily  adjusted. 


86  AMERICAN  METER  PRACTICE. 

The  small  cross  section  of  the  series  pole  pieces  allows 
the  coils  to  be  of  small  diameter,  thus  cutting  down  the 
length  of  wire  for  a  given  number  of  ampere  turns  and  re- 
ducing the  PR  losses  of  the  fields. 

The  impedance  coils  which,  in  a  single-phase  meter  of  this 
character,  have  more  inductance  than  resistance,  are  in 
series  with  the  shunt  field  circuit,  and  serve  to  displace  the 
phase  between  the  series  and  shunt  fields,  giving  the  ro- 
tating magnetic  field  necessary  for  the  rotating  of  the 
armature.  The  high  inductance  of  these  coils  reduces  the 
wattage  in  the  shunt  coil  to  a  minimum  in  this  particular 
meter  down  to  about  2  watts.  We  have  already  pointed 
out  the  manner  in  which  the  phase  of  the  potential  circuit 
is  made  to  lag  exactly  90  degrees  behind  the  current  in 
the  series  fields. 

The  case  of  the  meter  consists  of  a  heavy  cast  iron  back 
with  three  supporting  lugs.  The  cover  is  of  sheet  metal, 
hinging  to  the  case  by  means  of  a  slot  and  tongue,  and 
fastened  at  the  top  by  a  screw  over  the  head  of  which  passes 
the  seal  wire. 

The  cover  fits  into  a  groove  in  the  back  lined  with  soft 
rubber,  keeping  out  insects,  dust  and  moisture,  and  is  also 
provided  with  the  usual  window  for  reading  the  dials  and 
auxiliary  window  for  counting  the  revolutions  of  the  ar- 
mature. The  wires  do  not  enter  into  the  main  body  of  the 
meter,  but  are  fastened  into  a  binding  block  at  the  top  of 
the  case.  In  the  two-wire  meters,  one  leg  only  passes  into 
the  meter,  the  other  wire  of  the  circuit  feeding  the  shunt 
field  coils  by  a  half  tap.  The  three-wire  meters  have  the 
two  outside  legs  taken  into  the  meter  either  with  or  without 
the  half  tap  from  the  neutral. 

The  meters  are  designed  to  register  accurately  on  indue- 
tive  and  non-inductive  loads. 


DUNCAN  RECORDING  WATTMETER. 


87 


The  following  diagrams  are  explanatory  of  the  different 
ways  of  connecting  the  meters  for  various  classes  of  service. 
Other  ways  of  connecting  these  meters  for  various  kinds  of 
service  will  suggest  themselves  from  the  explanations,  given 
in  Chapter  II,  on  the  measurement  of  power  by  inductive 
meters  wherein  the  various  connections  for  two  and  three- 
phase  systems  were  given. 

Fig.  35,  shows  a  simple  two-wire  meter  service  in  which 
only  one  main  leg  is  taken  into  the  meter,  the  potential 
circuit  being  fed  by  a  half  tap  from  the  other  leg. 


FIG.  35. 

Fig.  36,  is  the  same  as  Fig.  35,  except  for  the  larger  lugs 
used  for  meters  over  100  ampere  capacity. 

The  three-wire  system  is  metered  by  taking  in  the  two 
outer  legs. 

Fig-  37,  the  potential  circuit,  is  fed  by  the  maximum 
voltage  of  the  system.  This  connection  is  used  for  meters 
of  low  efficiency  type;  the  regular  high  efficiency  meter  is 
connected  as  shown  in  Fig.  38. 

Regular  two-wire  meters  are  used  for  balanced  two  and 
three-phase  systems  and  for  balanced  two-phase  systems 


88 


AMERICAN  METER  PRACTICE. 


employing  four  wires,  as  shown  in  Figs.  39  and  40  respect- 
ively.    Of  course,  the  total  amount  of  power  consumed  in 


PROM 


TRANSFORMER 


TO 


TRANSLATING    DEVICES. 


FIG.  36. 


the  circuit  is  found  by  multiplying  the  register  of  the 
meter  by  the  number  of  phases. 


FROM                                          J 

TO 

TRANSFORMER.                              J  * 

TRANSLATING    DEVICES. 

JLf       V 

FIG.  37. 

This  meter  may  be  taken  as  a  type  representative  of 
quite  a  number  of  meters  such  as  the  Shallenberger, 
Shaeffer,  Guttman,  Packard,  all  of  which  employ  similar 


DUNCAN  RECORDING  WATTMETER. 


89 


principles,  but  of  course  differ  widely  in  mechanical  details. 
All  of  the  above,  however,  have  a  spring  mounted  jewel 
for  the  armature  support  in  common. 


FROM  TRANSFORMER 

_J 

TO  TRANSLATING  DEVICES. 

\ 

CD 

FIG.  38. 

In  this  one  point  all  these  types  of  meters  fail  to  fulfill  ideal 
conditions,  by  having  a  variable  frictional  support  for  the 


gn                          T0 

MOTOR. 

armature  which  changes  rapidly  for  the  worse  with  ill 
usage. 


90  AMERICAN  METER  PRACTICE. 

The  torque  in  this  type  of  meter  is  usually  small,  but  the 
ratio  between  torque  and  frictional  equivalent  may  be 
large  when  the  meter  is  new,  and  a  very  accurate  register  of 
load  through  wide  ranges  may  be  obtained.  The  meter  is 


FIG.  40. 


TO  MOTOR 


not  absolutely  air-tight,  and  is  subject  to  all  the  objections 
which  this  implies. 

What  may  be  said  of  this  meter  will  apply  generally  to  all 
meters  of  this  type. 


r^r        OF  THE 

UNIVERSITY 


CHAPTER  VIII. 

The    Duncan    Wattmeter — Commutated   Type,  for  Direct 

Current. 

Meters  of  the  commutated  type  for  use  on  direct  and 
alternating  current  systems  have  been  very  few  in  number; 
probably  the  best  known  is  the  Thomson  recording  watt- 
meter. 

The  Duncan  meter  has  recently  been  placed  on  the 
market,  and  its  electrical  and  mechanical  design  insure  for 
it  a  lasting  place  in  the  commercial  meter  field. 

The  meter  is  of  the  non-inductive  type  and  can  be  used  to 
register  direct  and  alternating  currents  with  equal  accuracy. 

Alternating  current,  whether  inductive  or  non-inductive, 
is  registered  without  a  change  in  calibration;  but  com- 
mutated types  of  meters  are  not  used  for  alternating  cur- 
rent as  much  as  inductive  type  meters,  owing  to  the  cheap- 
ness of  the  latter. 

In  principle  the  meter  is  a  Siemens  dynamometer,  the 
stationary  coils  of  which  are  energized  by  the  current 
flowing  in  the  circuit,  and  the  movable  coils  or  armature 
proportionally  to  the  potential  of  the  circuit  in  which  the 
meter  is  inserted.  There  is  no  iron  employed  in  the  series 
or  shunt  fields,  the  armature  is  wound  drum  fashion  over 
a  non-magnetic  skeleton  support  and  provided  with  com- 
mutator and  brushes.  The  field  coils  are  placed  in  mag- 
netic relation  to  the  armature,  and  the  whole  operates  as  a 
simple  motor,  the  current  flowing  energizing  the  fields 
the  potential  of  the  circuit,  the  shunt  field  coil  or 

91 


92 


AMERICAN  METER  PRACTICE. 


armature.  The  difference  in  operation  from  a  shunt 
motor  is  that  the  shunt  field  circuit  revolves  and  the 
series  circuit  remains  stationary. 

The  details  of  electrical  and  mechanical  design  will  prove 
more  interesting  than  a  repetition  of  the  theory  of  opera- 


FIG.  41. 


tion  of  meters  of  this  type  contained  in  the  Chapter  VI, 
on  Thomson  wattmeter,  with  which  we  are  already 
familiar. 

Fig.  41,  shows  meter  with  case  on  and  it  is  noticed  that 


DUNCAN  METER. 


93 


the  meter  hangs  from  the  top  lug  of  the  frame  and  is  lev- 
elled horizontally  by  the  side  lugs.  This  is  a  very  con- 
venient feature  in  installing,  as  the  workman  can  insert 
his  top  screw  and  then  hang  the  meter  on  it.  The  capacity 
and  voltage  of  the  meter  are  marked  in  plain  figures  on  the 


FIG.  42. 


case.  The  case  is  made  air-tight  and  is  hinged  at  its  lower 
extremity  to  the  meter  frame  as  shown  in  Fig.  45.  When 
the  case  is  lowered  the  hinge  holds  it  in  the  position  shown, 
and  when  it  is  lifted  a  little  it  comes  off.  This  is  a  very 
convenient  arrangement  for  inspection  and  testing. 


94 


AMERICAN  METER  PRACTICE. 


The  frame  is  made  of  a  single  aluminum  casting,  very 
light  and  rigid,  and  handsome  in  appearance.  Around  the 
front  edge  of  the  frame  is  a  groove  lined  with  felt  into  which 
the  cover  is  securely  clamped,  rendering  the  meter  dust  and 
insect  proof  when  closed.  A  seal  is  inserted  over  the  screw 


FIG.  43. 

holding  the  cover  closed,  rendering  access  to  the  meter  by 
unauthorized  persons  impossible,  except  by  breaking  the 
seal. 

Fig.  42,  is  a  front  view  of  the  interior  of  the  meter  with 
the  case  removed.     In  the  foreground  are  the  auxiliary, 


DUNCAN  METER. 


95 


or  starting  coil,  and  field  coils,  showing  their  relation  to  the 
armature  coils.     The  aluminum  brake  disk  is  shown  below 
revolving  between  the  poles  of  two  permanent  magnets. 
In  Fig.  43,  the  starting  coil  and  one  field  coil  are  removed, 


FIG.  44. 

showing  the  accessibility  of  the  armature,  and  a  still 
further  illustration  of  this  feature  is  seen  in  Fig.  44,  where 
the  essential  elements  of  the  meter  are  taken  apart  without 
disturbing  the  other  parts.  The  great  accessibility  to 
all  parts  of  the  meter,  and  the  ability  to  take  it 


96  AMERICAN  METER  PRACTICE. 

apart  by  the  removal  of  a  few  screws,  are  valuable  features 
when  repairs  or  inspection  are  necessary. 

The  perforated  cage  at  the  back  of  the  meter  encloses 
from  mechanical  injury  the  resistance  coil  in  series  with  the 
armature  circuit.  This  coil  is  wound  of  fine  resistance 
wire,  securely  held  in  place  and  thoroughly  insulated  from 
the  meter  frame.  The  round  hole  near  the  top  of  the 
meter,  Fig.  46,  is  for  the  entrance  of  the  feeding  wire  for 


FIG.  45. 

the  series  coils,  and  the  half  tap  for  the  potential  circuit  is 
led  in  from  the  top.  The  terminals  for  the  leading-in  wires 
are  mounted  on  a  wooden  block  just  inside  the  frame,  and 
are  inaccessible  when  the  meter  is  closed. 

Fig.  47  shows  the  case  removed  from  the  hinge,  but 
otherwise  is  a  repetition  of  Fig.  46. 

Figs.  48  and  49  are  views  of  the  revolving  element  and 
brushes  respectively.  The  worm  gear  at  the  top  of  the 


DUNCAN  METER. 


97 


98 


AMERICAN  METER  PRACTICE. 


DUNCAN  METER. 


09 


revolving  element  meshes  into  the  actuating  gear  of  the 
dial  train  in  the  usual  manner,  the  relation  of  the  gears  in 
the  dial  train  being  so  proportioned  that  all  sizes  of  meters 
register  directly  in  watt  hours  no  matter  what  the  speed  of 
the  revolving  element  may  be.  This  feature  eliminates 
errors  due  to  the  faulty  recording  of  the  multiplier  by  the 
meter  reader  or  office  clerk. 


FIG.  48. 

The  commutator  is  built  up  of  eight  segments  with  air 
insulation  between  the  bars,  and  is  composed  of  a  non-oxi- 
dizing metal.  The  brushes  bearing  on  this  commutator 
are  tipped  with  the  same  metal. 

The  armature  is  wound  with  very  fine  silk  covered  wire, 
with  a  large  number  of  turns  in  ?ach  section,  and  is 


100 


AMERICAN  METER  PRACTICE. 


thoroughly  insulated  from  the  shaft.  The  aluminum  brake 
disk  is  carried  just  above  the  hardened  steel  removable 
pivot  which  bears  on  the  spring  mounted  sapphire  bearing. 
The  spring  supporting  this  sapphire  is  so  proportioned  as  to 
cushion  the  blows  due  to  vibration  by  the  revolving  el- 
ement so  as  to  prolong  the  life  of  the  jewel.  The  exact 
strength  of  this  spring  is  a  very  important  feature.  The 
jewel  bearing  is  contained  in  an  ordinary  filister  head  screw 
which  can  be  easily  removed  for  inspection  or  repairs. 


BHBBSBEBHB9BI 


FIG.  49. 

The  field  coils  are  supported  on  studs  mounted  in  the 
frame  of  the  meter,  and  can  be  removed  as  shown  in  Fig. 
43.  The  whole  mechanical  design  of  the  meter  is  good,  and 
is  pleasing  to  the  eye,  embodying  at  the  same  time  neatness 
and  rigidity. 

The  dial  train  records  in  K.  W.  hours,  and  has  five  re- 
cording circles  in  a  straight  line.  The  figures  are  plain  and 


DUNCAN  METER.  101 

the  elimination  of  the  constant  or  multiplier  is  a  good 
feature. 

The  meters  are  manufactured  for  two  and  three-wire  cir- 
cuits; diagrams  of  the  various  connections  need  not  be 
given  as  they  are  the  same  as  those  shown  in  Chapter  II, 
for  the  various  classes  of  service. 

The  meter  will  be  considered  in  connection  with  the 
various  requisites  of  a  good  meter  given  in  Chapter  III. 

First:   Varying  Voltage  and  Load. 

On  loads  from  5  to  100  per  cent,  the  meter  has  a  very  good 
accuracy  curve,  but,  as  the  friction  is  equal  to  about  2  per 
cent,  of  full  load  torque  value,  any  increase  in  friction  has  a 
deleterious  action  on  accuracy.  The  mechanical  design 
of  the  meter  is  such,  however,  as  to  reduce  this  loss  to  the 
lowest  limit  for  meters  of  this  class.  The  voltage  is  reg- 
istered correctly  through  a  wide  variation,  no  appreciable 
error  arising  from  this  source. 

Second:    Varying  Frequency. 

As  the  meter  has  no  iron  in  its  magnetic  circuits,  the 
effect  of  varying  frequency  is  eliminated.  The  meter  needs 
no  change  of  calibration  for  circuits  of  7,200  or  16,000  alter- 
nations. 

Third:  Power  Factor. 

Variations  of  power  factor  are  met  accurately,  a  full 
description  of  power  factor  variations  for  non-inductive 
meters  being  given  in  Chapter  II. 

Fourth:    Wave  Forms. 

Owing  to  the  absence  of  iron  in  the  magnetic  circuits 
various  wave  forms  have  no  effect  on  the  accuracy  of  the 
meter. 


102  AMERICAN  METER  PRACTICE. 

Fifth:  Short  Circuit. 

A  short  circuit  on  the  lines  could  cause  a  rush  of  current 
which  would  largely  increase  the  magnetic  field  surround- 
ing the  field  coils  and,  if  heavy  enough,  cause  an  alteration 
of  the  magnetic  strength  of  the  permanent  magnets. 
There  is  no  provision  made  for  shielding  against  such  an 
occurrence. 

Sixth:  Permanence  of  Magnetic  Drag. 

The  manufacturers  claim  a  very  high  degree  of  perma- 
nence for  the  magnets  owing  to  a  special  process  which  is 
the  outcome  of  long  experience.  The  meter  has  not  been 
in  commercial  use  long  enough  to  verify  or  disprove  this 
statement. 

Seventh:    Torque. 

The  torque  of  the  meter  is  as  large  as  it  is  possible  to 
obtain  from  the  energy  expended  and  the  design  of  the 
meter.  The  torque  is  about  fifty  times  as  great  as  the 
counter  frictional  torque,  and  the  ratio  of  the  meter  is 
therefore  one  to  fifty.  From  Chapter  IV,  we  find  that  it 
would  not  be  good  design  to  further  increase  the  torque  at 
the  expense  of  further  energy  losses.  Hence,  the  meter 
fulfills  the  requirements  of  torque  for  the  given  frictional 
load. 

Eighth:   Friction  and  Friction  Balancing. 

Every  device  known  to  the  art  has  been  used  to  reduce 
friction  from  the  moving  parts,  but  as  all  commutated 
meters  have  a  brush  friction  which  it  is  impossible  to 
eliminate,,  besides  a  dial  friction  and  a  friction  due  to  the 
weight  oflhe  revolving  member  on  the  lower  bearing,  it  is 
not  entirely  frictionless.  A  compensating  coil  is  provided 


OF  THE 

UNIVERSITY 


DUNCAN.  METER. 

to  overcome  the  initial  friction  of  the  meter,  which  is  found 
to  be  about  2  per  cent,  of  full  load  torque  value.  This 
friction  compensator  is  not  adjustable. 

Ninth:    Energy  Losses. 

The  losses  in  the  potential  circuit  are,  for  the  no  volt 
series,  about  four  watts,  and  vary  in  the  field  circuits 
according  to  the  size  of  the  meter,  averaging  about  i  per 
cent,  of  the  capacity  of  the  meter  at  full  load. 

Tenth:  Armature  Support. 

The  armature  is  supported  on  a  highly  polished  sapphire 
bearing,  which  is  mounted  on  a  spring  of  such  tension  as  to 
produce  a  cushion  for  the  armature  to  all  jars  or  vibration 
to  which  the  meter  may  be  subjected.  This  type  of  bearing 
is  the  best  known  to-day,  where  end  bearings  are  used  at 
all.  The  hardened  steel  pivot  resting  on  the  sapphire  is 
ground  to  a  ball  point  and  highly  polished.  The  aluminum 
brake  disk  lightens  the  revolving  element  and  reduces  the 
friction  due  to  weight. 

Eleventh:    Air  Tight. 

The  construction  of  the  cover  and  its  seat  in  the  felt- 
lined  groove  render  the  meter  practically  air-tight.  It  is 
proof  against  acid  fumes,  dust,  insects,  etc.,  which  are  all 
so  injurious  to  meter  accuracy. 

Twelfth:    Temperature  Co-efficient. 

The  temperature  co-efficient  has  been  carefully  worked 
out  and  is,  for  all  practical  purposes,  unity. 

Thirteenth  :  Insulation  . 

The  insulation  between  wires  and  frame  exceeds  one 
megohm. 


104  AMERICAN  METER  PRACTICE. 

Fourteenth:  Mechanical  Features. 

In  the  various  figures  illustrative  of  the  meter,  the 
mechanical  features  were  dwelt  upon.  The  main  points 
are  rigidity  and  lightness,  and  this  meter  combines  both  in  a 
remarkable  degree. 

It  is  noted  from  the  foregoing  that  the  requisites  of  a 
good  meter  are  fulfilled  in  a  satisfactory  manner  by  the 
Duncan  commutated  meter,  and  it  is  a  worthy  example 
of  careful  design  and  well-thought-out  details. 


CHAPTER  IX. 
The  Stanley  Recording  Wattmeter. 

The  meters  heretofore  described  have  one  essential 
characteristic  feature  in  common,  a  jewel  bearing  for  sup- 
porting the  armature  shaft.  It  is  well  known  that  in 
alternating  current  meters  of  the  induction  type  the  alter- 
nations of  the  current  impart  a  vibration  to  the  armature 
shaft,  which  in  time  roughens  and  destroys  the  smoothness 
of  the  supporting  jewel  surface,  thereby  introducing  friction 
and  impairing  the  accuracy  of  the  record. 

In  the  Stanley  meter  the  lower  bearing  or  jewel  support 
is  entirely  dispensed  with,  the  armature  being  magnetically 
floated.  The  flat  aluminum  disk  armature  is  mounted  in  a 
soft  steel  core,  which  is  sucked  up,  so  to  speak,  to  a  position 
of  flotation  by  a  magnetic  system  composed  of  permanent 
magnets. 

The  shaft  is  aligned  in  a  vertical  position  in  this 
system  by  hardened  steel  wire  passing  through  phosphor 
bronze  guide  rings  in  center  of  armature  core. 

These  guide  rings  are  very  accurately  placed,  so  that  the 
axis  of  rotation  corresponds  as  closely  as  possible  with  the 
axis  of  the  magnetic  system.  Upon  the  correctness  of  this 
adjustment  depend  in  great  measure  the  frictionless  qual- 
ities of  the  support. 

Fig-  50  presents  a  view  of  the  exterior  of  the  meter.  Fig. 
51  shows  the  front  part  removed,  disclosing  the  front 
compartment  containing  the  permanent  magnets,  etc. 

In  the  foreground,  Fig.  5 1 ,  are  seen  the  permanent  mag- 
nets with  their  poles  in  contact  with  pole  pieces  pierced 

105 


106  AMERICAN  METER  PRACTICE. 

with  holes,  with  projecting  rings  corresponding  to  like 
rings  in  the  armature  core.  This  enables  the  core  to  assume 
a  definite  position  in  the  magnetic  system.  A  clear 
understanding  may  be  had  of  this  magnetic  relation 
if  we  liken  it  to  that  of  a  solenoid,  the  position  assumed 


FIG.  50. 

MODEL    G METAL    ENCLOSED. 

by  an  iron  core  in  the  solenoid  corresponding  to  the  mag- 
netic flotation  of  the  armature  shaft  in  the  flux  established 
by  the  permanent  magnets. 

Adjustable    pole    pieces    are   provided  which,  in    con- 
junction   with    the     armature    disk    revolving    between 


STANLEY  RECORDING  WATTMETER.  107 

them,  furnish  a  magnetic  brake  of  the  usual  character 
for  the  meter.  These  pole  pieces  are  adjusted  vertically, 
thereby  varying  the  reluctance  of  the  air  gap,  and,  the 
magnetic  flux  passing  through  it,  resulting  in  a  like 
variation  of  the  power  of  the  braking  action. 


FIG.  51. 

FRONT  VIEW  OP  SUPPORTING  FRAME,  SHOWING  BRAKE 
MAGNETS,  DIAL,  ETC. 

Fig.  52  shows  in /more  detail  the  magnetic  suspension 
elements  of  the^recent  model  G  meter,  and  the  method 
of  suspension  of  tffe ^magnetically  floated  armature. 

The    magnetic  /  suspension     elements    consist    of    the 


108  AMERICAN  METER  PRACTICE. 

1 

permanent    magnet     Y,    and    the    steel    plugs    or    pole 
bushings,  A  and  B. 

The  rotating  parts  floated  in  air  are  the  aluminum  disk 
and  the  soft  steel  vertical  shaft,  called  suspension  core, 
to  which  the  disk  is  rigidly  secured. 

The  lower  end  of  the  suspension  core  is  flanged  larger, 
while  the  upper  end  is  turned  smaller  in  diameter  than 
the  body  of  the  core. 


FIG. 


The  flanged  lower  end  of  the  suspension  core  enters  a 
cup  formed  in  the  lower  pole  bushing  B\  its  upper  end, 
when  in  magnetic  suspension,  is  just  inside  of  a  recess 
in  the  upper  pole  bushing  A . 

The  difference  in  diameters  between  the  flange  of  the 
suspension  core  and  the  cup  in  the  lower  pole  bushing  B, 
as  also  between  the  upper  end  of  the  suspension  core  and 


STANLEY  RECORDING  WATTMETER.  109 

the  recess  in  the  upper  pole  bushing  A ,  is  such  that  there 
is  a  predetermined  space  all  around  the  flange  in  pole 
flushing  B,  and  all  around  the  upper  end  of  the  core  in 
pole  bushing  A . 

When  the  suspension  magnet  is  not  in  place  the 
flanged  end  of  the  suspension  core,  due  to  gravitation, 
will  naturally  rest  on  the  surface  of  the  cup  in  pole 
bushing  B\  but,  due  to  difference  in  diameters,  it  will 
not  touch  the  circumference  of  the  cup  at  any  point, 
there  being  an  air  space  between  the  periphery  of  the 
flange  and  the  circumference  of  cup. 

When  the  suspension  magnet  is  not  in  place,  and  when 
the  lower  end  of  suspension  core  rests  on  the  surface  of 
the  cup  in  pole  bushing  B,  the  upper  end  of  the  core 
will  be  slightly  below  the  lower  edge  of  the  upper  pole 
bushing  A. 

Magnetism  passes  between  the  ends  of  the  magnetized 
plugs  (pole  bushings  A  and  B),  attracts  the  steel  suspen- 
sion core,  with  the  disk  attached,  in  an  upward  direction, 
lifts  the  flanged  lower  end  of  the  suspension  core  from 
contact  with  the  surface  of  the  cup  in  the  lower  pole 
bushing  B,  and  carries  the  upper  end  of  the  suspension 
core  into  the  recess  in  the  upper  pole  bushing  A . 

By  the  laws  of  magnetism,  the  magnetic  field,  into 
which  the  suspension  core  with  its  attached  disk  is  thus 
attracted,  acts  uniformly  upon  the  suspension  core,  hold- 
ing the  rotating  parts  in  a  predetermined  definite  position  in 
space,  free  from  mechanical  support  or  contact  of  any  kind. 

The  actuating  part  of  the  meter  is  contained  in  a  closed 
iron  compartment  which  shields  it  magnetically  from  out- 
side influence^.  A  slot  in  the  case  permits  the  arma- 
ture to  revolve  between  the  poles  established  by  the 

series  and  shunt  field  coils  in  circuit  with  the  energy  to  be 
/ 


110  AMERICAN  METER  PRACTICE. 

measured.  The  field  coils  are  ribbon-wound  and  mounted 
one  below  and  one  above  the  disk.  The  shunt  field  coils ,  four 
in  number,  are  carried  on  a  laminated  yoke,  having  pro- 
jecting pole  pieces  straddling  the  ribbon-wound  series  coils. 

The  method  of  obtaining  the  "lag  compensation"  for 
the  potential  circuit  differs  in  this  meter  from  the  usual 
form  of  impedance  coil  with  short-circuited  secondary. 

The  potential  circuit  is  wound  around  a  laminated 
magnetic  yoke  having  two  air  gaps  in  its  magnetic  circuit. 
The  reluctance  of  these  air  gaps  is  so  proportioned  that 
an  initial  lag  angle  of  about  eighty  degrees  is  obtained. 
The  introduction  of  the  armature  disk  into  these  air  gaps 
is  so  designed  that  the  resultant  eddy  currents  set  up 
therein  react  upon  the  magnetic  flux  in  such  a  manner 
as  to  displace  the  effective  flux  by  ninety  degrees  from 
the  impressed  voltage  of  the  system. 

This  phase-angle  depends  upon  the  conductivity  of  the 
inserted  closed-circuited  disk,  and  is  the  complement  of 
the  angle  of  lag  of  the  energizing  coil. 

The  revolving  magnetic  field  set  up  between  the 
potential  and  current  fields,  cutting  across  this  closed 
secondary  or  armature,  induces  eddy  currents  therein.  The 
reaction  of  these  currents  on  the  primary  field  produces 
rotation  of  the  armature  at  a  speed  proportional  to  the 
energy  passing. 

The  service  feeds  the  meter  on  the  left  side,  the  disk 
appearing,  when  observed  from  above,  to  revolve  in  the 
same  direction  as  the  hands  of  a  clock.  The  meter  is  sealed 
so  as  to  be  air-tight,  and  is  guaranteed  by  the  makers  for  a 
period  of  three  years.  An  especially  good  feature  about 
the  design  of  this  meter  is  the  absolute  exclusion  of  dust, 
insects,  etc.,  and  it  is,  in  this  respect,  ahead  of  the  meters 
now  on  the  market. 


UNIVERSITY   J 


STANLEY  RECORDING  WATTMETER.  Ill 


The  energy  consumed  in  the  potential  circuit  is  about 
2  J  watts;  the  PR  losses  in  the  fields  are  small,  owing  to  the 
small  radius  of  the  winding    and  consequent  short  length 
of  conductor.     Great  accuracy  is  claimed  for  this  meter. 
As  the  meter  is   suitable    only   for   alternating   current, 
the   usual   methods   of   connecting   it   in   circuit   are  the 
same  as  apply  to  all  induction  meters.     The  absence  of  a 
compensating  device  for  friction  shows  how  much  the  ratio 
of  frictional  equivalent  to  torque  is  reduced  by  this  method 
of  supporting  the  armature  spindle.     A  slight  oscillation  is. 
noticed  in  the  armature  disk  when  no  load  is  on  which  is 
caused  by  the  slight  difference  in  radical  conductivity  of 
the  disk  in  which  eddy  currents  are  generated.     A  zero 
point   is    soon  reached   and  the  oscillation  stopped.      It 
will  prove  of  great  interest  to  watch  the  commercial  life 
of  this  meter  which  in  so  many  respects  is  a  radical   de- 
parture from  the  ordinary  types.     Its  history  is  now  in  its 
infancy,  and  no  trustworthy  conclusions  can  be  drawn  as  to 
its  life  without  more  extended  service.     The  meter  is  man- 
ufactured in  the  usual  commercial  sizes  and  for  various 
'-equencies.     This  meter  promises   to   fill  more  fully  the 
requisite  of  a  good  meter  than  any  other  type,  owing  to  the 
permanence  of  its  fractional  equivalent.    The  effects  of  short 
circuits  on  the  permanent  magnets  are  entirely  eliminated, 
as  the  field  coils  are  mounted  behind  a  steel  shield  which 
effectually  keeps  any  magnetism  from  straying  beyond  it. 
The  permanent  magnets  are  long  and  the  pole  pieces  are 
held  in  an  absolute  relation  by  being  mounted  in  a  brass 
yoke.     This  prevents  any  widening   of   the  air  gap  and 
consequent  change  in  meter  speed.      While  the  torque  of 
this  meter  is  not  any  larger  than  many  others,  the  fric- 
tional equivalent  is  so  exceedingly  small  and  so  constant 
that  a  very  high  degree  of  permanent  accuracy  is  obtained 


112  AMERICAN  METER  PRACTICE. 

on  very  light  loads.  The  supporting  of  the  shaft  by  a 
magnetic  flotation  removes  all  vertical  friction,  and  the 
horizontal  friction  of  the  guides  is  practically  eliminated 
by  placing  the  armature  core  in  the  exact  center  of  mag- 
netic stress,  so  that  the  pull  in  every  side  is  balanced. 
The  friction  of  the  dial  train  is  probably  greater  than  the 
other  friction,  but  is  inappreciable;  hence,  it  is  unnecessary 
to  have  a  frictional  balance. 

The  absolute  permanence  of  the  armature  support 
renders  the  meter  impervious  to  vibration,  and  as 
it  is  hermetically  sealed,  all  acid  fumes,  dust,  etc.,  are 
excluded,  and  the  elements  of  the  meter  retain  their  same 
relation  towards  each  other  for  a  long  period  of  time. 


CHAPTER  X. 
The  Guttman  Wattmeter. 

Induction  wattmeters  of  different  makes  have  their  main 
characteristics  in  common,  viz.,  a  series  field  in  quadrature 
with  a  potential  circuit  and  some  form  of  friction  com- 
pensator. 

The   Guttman  wattmeter  in  its  present  form  possesses 


FIG.  53. 

considerable  merit,  and  has  a  very  pleasing  mechanical 
appearance.  Fig.  53  shows  the  meter  with  case  on,  and 
Fig.  54  with  case  removed. 


113 


114 


AMERICAN  METER  PRACTICE. 


A  better  idea  of  the  rotating  mechanism  of  the  meter 
is  obtained  in  Fig.  55,  wherein  the  cover,  dial  and  perma- 
nent magnet  are  removed. 

Like  the  Stanley  meter,  the  armature  and  retarding  disk 
are  combined  in  one  to  form  the  rotating  armature. 

In  the  old  style  Guttman  meter,  the  armature  took  the 
form  of  a  long  spirally  slotted  cylinder,  and  a  separate  disk 
was  acted  upon  by  a  permanent,  magnet  to  furnish  the 
brake. 


FIG.  54. 

The  same  principle  of  operation  is  used  in  the  new  meter 
as  in  the  old,  except  that  the  spirally  slqtted  cylinder  and 
disk  are  combined  in  one.  The  torque  of  the  meter  is 
obtained  by  the  interaction  of  £he  slotted  armature  disk 
with  the  magnetic  fluxes  set  up  by  a  laminated  shunt 
magnet  and  a  small  set  of  series  fields.  The  armature  is 
carried  on  a  short  shaft  having  a  ball  shaped  pivot  to  fit 


GUTTMAN  WATTMETER. 


115 


the  supporting  jewel,  and  is  geared  by  means  of  a  worm  at 
its  upper  end  to  the  usual  dial  train.  The  whole  armature 
weighs  only  about  five-eighths  of  an  ounce,  so  that  the  wear 
on  the  jewel  bearing  is  very  slight.  The  shunt  and  series 


FIG.  55. 

magnetic  circuits  are  composed  of  two  parts ;  a  laminated 
steel  magnet  body  carrying  the  shunt  field  coil,  and  the 
"bridge"  carrying  the  series  coils. 


116  AMERICAN  METER  PRACTICE. 

On  the  inner  side  of  the  shunt  field  magnet  is  held  the 
compensating  device,  which  is  adjustable  by  means  of  a 
screw.  A  good  view  of  the  shunt  and  series  magnetic 
fields  is  obtained  in  Fig.  56,  which  shows  their  mechanical 


FIG.  56. 

relation  to  each  other  plainer  than  any  amount   of  de- 
scription could. 

In  the  series  field  magnetic  circuit  we  have  two  air  gaps 
which  add  slightly  to  the  reluctance  of  the  entire  magnetic 


GUTTMAN  WATTMETER.  117 

circuit,  but  this  addition  is  so  slight  as  to  scarcely  affect  the 
self-induction  of  the  shunt  field  coil. 

The  compensation  of  the  meter  for  inductive  loads  is 
effected  by  means  of  a  heavy  copper  band  with  a  small  gap 
in  it,  attached  to  the  bridge  on  the  lower  side.  This  gap 
is  closed  by  means  of  a  resistance  wire  of  such  size  as  to 
permit  enough  induced  current  to  flow  to  effect  the  desired 
compensating  effect. 

The  secondary  current  induced  in  the  band,  when  of  the 
correct  amount,  reacts  upon  the  field  just  enough  to  cause 
it  to  be  in  apparent  quadrature  with  the  impressed  electro- 
motive force.  The  secondary  induced  currents  in  the 
armature  will  then  be  of  the  right  phase  to  measure 
the  true  energy  passing  in  the  circuit  when  acted  upon 
by  the  flux  from  the  series  coils.  For  low  frequencies 
the  resistance  of  this  connection  across  the  gap  in  the 
band  is  decreased,  and  it  is  made  adjustable  for  different 
frequencies. 

The  series  coils  are  held  by  means  of  aluminum  clamps, 
and  are  placed  in  such  position  as  to  obtain  the  maximum 
rotating  effect  on  the  disk. 

Each  coil  is  1.4  inches  long  and  1.25  inches  in  diameter; 
being  small,  they  have  very  little  resistance  or  self- 
inductance. 

The  permanent  magnet  for  the  retarding  effect  is,  in  the 
main,  of  the  usual  form,  but  differs  slightly  in  its  shape 
from  either  the  Thomson  or  Duncan. 

The  meters  are  sent  out  sealed  from  the  factory,  and  the 
connections  are  made  to  the  service  wires  without  getting 
into  the  interior  of  the  meter. 

The  meters  are  made  in  two  and  three- wire,  and  are  con- 
nected in  circuit  in  the  same  manner  that  any  induction 
meter  would  be. 


118  AMERICAN  METER  PRACTICE. 

For  all  meters  above  fifty  amperes  a  series  transformer 
is  used,  and  a  potential  transformer  is  employed  where 
more  than  250  volts  are  required. 

The  mechanical  features  of  the  meter  are  excellent;  it  is 
light,  compact,  well  made,  and  is  dust  and  insect  proof. 
There  has  hardly  been  time  as  yet  to  determine  its  dura- 
bility. The  dial  reads  directly  in  watt  hours,  and  the 
ratios  of  the  armature  shaft  and  dial  train  are  changed  to 
suit  the  different  speeds  in  large  and  small  meters. 

The  meter  has  a  good  temperature  co-efficient  and  low 
watt  losses  in  the  shunt  and  field  circuits.  The  loss  in  the 
potential  circuit  varies  with  the  voltage  and  frequency, 
but  ranges  from  J  to  ij  watts.  The  field  losses  average 
two  watts  at  full  load.  Owing  to  the  lightness  of  the 
armature,  the  fractional  torque  is  low,  and  accuracy  is 
claimed  on  two  per  cent,  of  the  rated  capacity. 


CHAPTER  XI. 
The  Westinghouse  Induction  Meter. 

Probably  one  of  the  earliest  forms  of  induction  meter 
used  for  commercial  purposes  was  the  Shallenberger  ampere- 
hour  meter.  This  meter  has  become  obsolete  in  modern 
practice,  although  it  may  still  be  found  connected  in  a 
number  of  instances. 

The  Westinghouse  company,  during  the  past  few  years, 
has  been  manufacturing  a  meter  that  registers  watt-hours 
instead  of  ampere-hours.  It  is  made  single  and  multi- 
phase in  all  standard  frequencies. 

Fig.  57  shows  the  exterior  of  a  single-phase  meter, 
and  gives  a  good  idea  of  the  neatness  and  compactness 
of  its  mechanical  features. 

In  theory  the  meter  is  similar  to  all  induction  meters  in 
that  the  field  maintained  by  the  potential  circuit  is  in 
quadrature  to  the  series  field  when  registering  non-inductive 
loads. 

The  laminated  sheet  steel  yoke  carrying  the  shunt  and 
series  windings  is  clearly  shown  in  Fig.  58.  It  will  be 
noticed  that  the  shunt  coils  are  two  in  number,  and  are 
•carried  on  the  half  of  the  yoke  from  which  projects  two 
annular  shaped  pole  pieces.  The  series  field  consists  of  a 
few  turns  of  wire  wound  round  an  upwardly  projecting 
pole  piece. 

In  series  with  the  potential  winding  is  an  impedance 
coil  which  approximately  places  the  shunt  field  coil  in 
quadrature  with  the  series  field.  A  short-circuited 
secondary  winding  wound  over  the  potential  coils  is 

119 


120 


AMERICAN  METER  PRACTICE. 


adjusted  through  the  resistance  coil  shown  in  Fig.  58,  in 
such  a  manner  as  to  place  the  fields  in  exact  quadrature. 

In  this  secondary  winding  is  placed  a  resistance  bar  on 
which  slides  the  connector  A,  Fig.  58,  which  moves  to  right 


FIG.  57. 

or  left  to  furnish  a  balancing  friction  compensator.  Before 
adjusting  the  meter  to  run  under  load,  an  adjustment  for 
frictional  load  should  be  made.  Move  the  connector  At 
Fig.  58,  to  the  right  until  the  meter  runs  with  a  positive 
movement  without  any  load.  The  steadiness  of  this 


WESTINGHOUSE  INDUCTION  METER. 


121 


movement  of  the  meter  disk  will  determine  whether  any 
stickiness  or  intermittent  friction  exists.  When  this  is 
determined  the  sliding  contact  should  be  moved  to  the  left 
until  the  meter  stops. 

The  meter  may  then  be  adjusted  on  full  load,  and 
for  all  loads  down  to  about  2  per  cent,  of  the  full  load. 
Coils  may  be  cut  in  or  added  to  the  closed  secondary 
surrounding  the  shunt  field  coils  in  order  to  secure  the 
proper  position  of  the  sliding  contact  A,  Fig.  58,  near  the 


FIG.  58. 

middle  of  the  resistance  bar  on  which  it  slides.  The 
closed  secondary  coils  are  wound  in  such  a  manner  as  to 
allow  of  their  being  easily  connected  to  make  the  meter 
correct  on  frequencies  varying  over  a  wide  range  as  from 
7,200  to  16,000. 

The  revolving  element  consists  of  a  short  shaft  on  which 
is  mounted  an  aluminum  disk  of  small  diameter,  this 
aluminum  disk  revolves  between  the  poles  projecting  in- 
ternally from  the  magnetic  yoke.  The  magnetization  set 


122  AMERICAN  METER  PRACTICE. 

Tip  by  the  current  flowing  in  the  shunt  and  series  fields 
acts  upon  the  aluminum  disk,  creating  therein  induced 
currents  which  react  on  the  rotating  field  in  a  manner  to 
revolve  the  disk  with  a  torque  varying  according  to  the 
energy  flowing. 

When  the  load  on  the  meter  is  non-inductive,  the  current 
in  the  shunt  field  lags  90  degrees  behind  the  E.M.F.  of  the 
circuit.  As  the  power  factor  decreases,  the  shunt  field 
becomes  more  in  phase  with  the  E.M.F.  of  the  circuit. 
Hence,  the  meter  registers  accurately  inductive  or  non- 
inductive  loads. 

The  latest  form  of  meter  has  a  ball  bearing  support. 
The  end  of  the  armature  shaft  contains  a  cup-shaped 
jewel  which  rests  on  a  small,  highly  polished  steel  ball, 
which  is,  in  turn,  supported  in  a  cup-shaped  jewel  bearing. 
The  steel  ball  constantly  turns  as  the  meter  revolves,  and 
furnishes  an  excellent  support.  In  fact,  so  accurate  are 
these  meters  that  a  straight  line  accuracy  curve  is  ob- 
tained from  2  per  cent,  to  100  per  cent,  load,  a  slight  falling 
off  is  observed  after  full  load,  and  on  50  per  cent,  over- 
load the  meter  is  from  J  to  i  per  cent.  slow. 

The  three-wire  meters  are  provided  with  two  field  coils 
wound  over  the  projecting  pole  piece,  one  in  series  with 
each  outside  leg  of  the  three-wire  system.  Otherwise,  the 
meters  are  identical  with  the  two-wire  type.  The  shunt 
field  coil  is  connected  between  the  neutral  and  an  outside 
leg.  Polyphase  meters  have  two  distinct  single  phase 
units,  placed  one  above  the  other,  and  acting  on  a  single 
armature  having  two  disks.  These  two  single  phase  units 
are  connected  up  exactly  as  though  they  were  separate 
meters  under  separate  covers.  The  meter  case  is 
necessarily  longer  than  the  single  phase  units,  but  other- 
wise the  meters  are  the  same  in  their  make-up. 


WESTINGHOUSE   INDUCTION  ME 


The  regulating  device  consists  of  the  usual  permanent 
magnet,  which  acts  as  a  brake  on  the  disk  which  revolves 
between  its  poles.  The  meter  is  made  fast  or  slow  by 
moving  it  in  or  out.  These  magnets  are  given  a  special 
treatment  which  ensures  their  remaining  permanent  for 
a  number  of  years.  The  dial  face  is  provided  with  five 
dials  which  read  from  right  to  left.  A  complete  revolution 
of  the  first  right  hand  dial  indicates  one  kilowatt  hour,  and 
the  succeeding  dials  increase  in  multiples  of  ten.  No 
multiplier  is  used,  and  the  meters  read  directly  in  kilowatt 
hours.  The  meters  are  connected  for  various  circuits  as 
outlined  in  Chapter  III.  The  current  consumed  in  the 
potential  circuit  varies  from  i£  watts  to  2  watts,  and  the 
loss  in  the  fields  at  full  load  is  negligible  owing  to  the 
small  number  of  turns  and  the  small  radius  of  the  coils. 

The  torque  of  the  meter  is  small,  but  large  in  proportion 
to  the  weight  of  the  revolving  element  which  is  unusually 
light.  The  ratio  between  torque  and  friction  of  the 
meter  is  large,  hence  the  great  degree  of  accuracy 
obtained  over  a  wide  range  of  loads  and  on  extremely  light 
loads. 

The  meter  box  is  sealed  so  that  it  is  air-tight  and  dust 
and  insect  proof.  The  inleading  wires  do  not  enter  the 
body,  but  are  designed  to  connect  under  binding  posts 
contained  at  the  top  of  the  meter. 

The  cast  iron  body  containing  the  meter  forms  a  thorough 
shield  from  outside  magnetic  influences.  The  presence 
of  strong  external  magnetic  fields,  has  no  influence  on  the 
accurate  registration  of  the  meter. 

It  will  be  of  interest  to  watch  the  life  of  the  ball  bearing 
armature  support ;  it  has  every  indication  of  being  a  vast 
improvement  over  the  pointed  steel  shaft  both  in  point  of 
life  and  of  lower  f fictional  value. 


CHAPTER  XII. 

General  Management  of  the  Meter  Department — Records — 
Testing — General  Policy. 

The  general  operation  of  a  meter  department  divides 
itself  primarily  into  two  distinct  branches;  the  keeping 
of  records,  and  the  technical  branch  which  includes  testing, 
repairs,  etc.  In  large  central  stations  the  meter  depart- 
ment employs  a  large  number  of  men,  who  are- organized 
with  a  clerical  and  technical  force.  In  some  stations  the 
record  part  is  kept  distinct  from  the  technical  part,  the 
records  being  a  branch  of  the  auditing  department.  It  is 
general  practice,  however,  for  the  meter  department 
to  keep  all  its  own  records  and  be  responsible  as  a  depart- 
ment for  everything  which  eminates  from  it.  There  is 
necessarily  a  close  bond  between  this  department  and  the 
auditing  department,  and  the  place  where  the  work  of  the 
one  is  turned  over  to  the  other  varies  in  different  central 
stations.  The  keeping  of  any  kind  of  records  has  been 
worked  out  along  several  well  defined  lines,  the  alpha- 
betical system  being  most  generally  adopted,  as  fur- 
nishing the  most  convenient  natural  divisions.  The 
treachery  of  the  memory  is  proverbial,  and  it  is  well  to 
trust  nothing  of  the  least  moment  to  verbal  communi- 
cation; hence,  the  keeping  of  records  not  only  involves 
the  keeping  of  ledger  accounts,  but  all  of  the  minute 
details  of  the  business.  If  the  business  be  small,  it  is 
possible  to  carry  it  on  with  less  "red  tape"  than  would 
otherwise  be  necessary,  but  as  the  number  of  details 

124 


RECORDS.  125 

increase,  it  is  essential  to  have  some  well  defined  system 
along  which  to  work  out  and  record  them.  Each  central 
station  has  its  own  peculiar  forms  and  systems;  therefore, 
what  is  here  written  must  be  considered  as  illustrative  of 
simply  one  system  which  has  been  found  to  fulfill  the 
demands  of  the  service. 

Let  us  assume  that  the  central  station  business  is 
divided  into  three  main  departments,  the  engineering, 
contracting  and  auditing.  The  meter  department  lies 
under  the  head  of  the  engineering  department,  but  is 
in  close  touch  with  the  other  two.  The  contracting 
department,  we  will  assume,  has  charge  of  soliciting 
new  business,  rating,  etc.,  and  is  a  department  which 
represents  the  company's  policy  and  interests  to  its 
customers. 

All  communications  touching  new  installations,  cut- 
offs, extensions  of  service,  etc.,  are  received  from  the  con- 
tracting department  to  be  acted  upon  by  the  engineering 
department.  It  is  good  practice  to  have  all  such  orders  go 
to  a  special  clerk  (or  clerks)  in  the  engineering  department 
who  disposes  of  them  according  to  their  character.  Orders 
issued  to  the  meter  department,  when  fulfilled,  are  returned 
O.  K.  to  the  clerk,  and  checked  up  against  the  original 
order  from  the  contracting  department.  Any  discrep- 
ancy is  at  once  noted  and  the  proper  steps  taken  to  remedy 
the  error,  or  orders  may  be  issued  directly  to  the  meter 
department  from  the  contracting  department.  In  either 
event  the  order  is  re-issued  as  a  record  in  that  department. 
After  an  order  for  an  installation  has  been  received,  there 
are  various  orders  for  lamps,  meters,  etc.,  to  be  issued  by 
the  meter  department  to  the  stock-keeper.  All  of  these 
minor  orders  are  returned  O.  K.  when  fulfilled,  and  a  record 
is  kept  for  reference. 


126  AMERICAN  METER  PRACTICE. 

To  avoid  the  issuance  of  a  great  number  of  lamp  orders 
during  the  day,  each  installation  man  is  issued  an  amount  of 
lamp  stock  sufficient  for  one  day's  needs.  On  his  daily 
report  the  name,  address  and  number  of  lamp  used  for 
installation  are  recorded,  and  the  total  must  balance  with 
the  number  of  lamps  returned  in  the  original  order.  This 
system  has  been  found  to  be  exceedingly  satisfactory  and 
labor  saving,  and  any  shortages  are  easily  checked  at  the  end 
of  the  day.  The  meter  orders  are  returned  by  the  installa- 
tion man,  the  number,  size,  etc.,  of  the  meter  being  checked 
and  0.  K'd  by  the  store-keeper  on  the  issuance  of  the  meter 
from  his  stock.  In  this  way  a  double  check  is  placed  on  the 
order  and  the  assurance  of  obtaining  the  meter  ordered. 
The  daily  report,  therefore,  of  the  installation  man  is  a 
check  and  record  of  the  fulfillment  of  his  orders  for  that 
day.  It  is  general  practice  to  keep  account  of  the  meter 
as  an  individual  meter  on  the  card  system,  the  card  telling 
when  the  meter  was  received,  when  first  installed,  and  its 
general  history  thereafter.  This  may  prove  interesting  to 
one  who  is  collecting  data  on  repair  and  maintenance  of 
meters,  but  otherwise  is  not  essential.  The  meter  should 
be  treated  as  an  arc  lamp,  or  any  other  piece  of  apparatus. 
Any  peculiarity  in  running  is  readily  traceable  to  some 
source.  There  should  be  no  such  thing  as  an  erratic 
meter;  one  that  retains  peculiar  characteristics  which 
would  form  interesting  history. 

If  a  new  meter  is  sent  into  service,  and,  after  being 
installed  several  months,  has  to  be  brought  in  for  repairs, 
the  fields,  armature,  or  any  part  of  it,  may  be  changed  and 
the  meter  thus  loses  its  original  individuality.  When  re- 
tested  and  sent  out  it  should  conform  to  the  known  effi- 
ciency curve  obtainable  from  the  type  of  meter.  If  it  does 
not  give  this  efficiency  curve,  the  trouble  which  exists- 


RECORDS.  127 

somewhere  must  be  found  and  remedied.  The  life  of  the 
meter  can  be  prolonged  indefinitely  by  the  renewal  of  parts. 
In  five  years  it  is  possible  for  only  the  frame  to  be  in  the 
same  condition  as  when  first  installed.  There  should  be  no- 
such  thing  as  the  history  of  a  "cranky"  meter,  as  that 
expression  merely  means  insufficient  knowledge  or  care  in 
locating  its  troubles. 

An  indexed  list  of  tested  stock,  giving  the  sizes,  numbers, 
voltage,  etc.,  of  the  meters  ready  for  insulation  is  all  that 
is  necessary,  the  meter  when  ordered  out  being  scratched 
off  the  list.  The  record  of  the  meter  after  it  is  installed  is 
preserved  on  the  meter  slip  as  well  as  in  the  order  book. 
The  meter  number  is  not  only  a  guide  to  the  meter  reader 
and  bill  clerk,  but  also  enables  the  consumer  to  check  from 
his  bill  against  the  meter  number  in  his  premises.  From  the 
foregoing  it  is  clear  that  the  keeping  of  an  individual  record 
of  each  meter  as  a  meter  is  superfluous  and  involves  labor 
which  can  easily  be  avoided.  The  systematic  reading 
and  recording  of  the  registers  of  the  consumers  is  carried 
on  by  means  of  meter  slips,  giving  the  name,  address,  meter 
number,  size,  etc.,  of  each  meter  on  the  system.  The 
sample  meter  slip,  Fig.  59,  is  one  which  was  in  use  several 
years  in  a  large  central  station,  and  was  found  satis- 
factory. If  the  reader's  slip  be  the  only  record  of  the  read- 
ing, some  form  of  ledger  is  usually  kept  to  preserve  the 
reading  in  case  of  accident  to  the  slip.  It  is  much  more 
convenient,  however,  to  run  a  duplicate  set  of  slips  which 
will  be  exact  copies  of  the  reader  slip.  The  advantages  of 
such  a  duplicate  record  are  many.  There  is  always  in 
the  office  a  duplicate  set  of  the  readings  of  a  customer  for 
reference,  the  slips  serve  to  replace  each  other  in  the 
event  of  either  being  lost  or  misplaced,  and  further,  the 
slips  are  more  flexible  than  the  ledger.  It  is  a  recognized 


128 


AMERICAN  METER  PRACTICE. 


practice  in  large  stations  to  read  approximately  the 
same  number  of  meters  each  day  and  have  them  listed  ac- 
cording to  their  situation  so  as  to  avoid  as  much  walking  as 


FIG.  59. 

possible.  These  meters  are  indexed  and  arranged  alpha- 
betically while  they  are  in  their  cases,  and  also  numbered 
according  to  location,  so  the  reader  has  no  difficulty  in 


OF  THE 

UNIVERSITY 

*£fUFOR^ 


RECORDS. 

making  up  his  route.  Any  new  customer  in  the  route 
is  given  the  decimal  part  of  a  number  in  between;  for 
example,  36.1  would  be  the  number  given  a  customer 
coming  between  36  and  37  in  a  given  route  and  36.2 
an  additional  customer  between  36  and  37.  After  the 
route  is  read  the  readings  are  copied  in  the  office  on  the 
duplicate  slips  and  rendered  from  them  into  a  ledger  file 
which  serves  as  a  journal,  from  which  to  post  the  net  bills 
into  the  consumer's  ledger.  The  renderings  in  this  file  are 
checked  from  the  reader's  slips,  so  that  any  errors  in  copy- 
ing the  readings  to  the  duplicate  slips  and  errors  in  render- 
ing are  checked  at  the  same  operation.  This  system  has 
been  found  to  give  eminent  satisfaction,  and  furnishes  a 
check  on  each  stage  of  the  work  without  checking  each 
individual  operation.  The  sample  ledger  file  sheet,  Fig.  60, 
is  shown,  from  which  a  clearer  idea  can  be  obtained  of  the 
manner  of  rendering  the  bill.  The  dividing  line  between 
this  clerical  work  of  auditing  and  meter  departments  is 
usually  drawn  at  the  K.  W.  column  on  the  rendering  sheet, 
the  making  out  of  the  bills,  posting,  etc.,  being  done  in  the 
auditing  department.  Of  course,  this  is  a  mere  arbitrary 
practice  and  is  not  followed  in  many  stations.  Each  bill 
should  receive  the  scrutiny  and  judgment  of  the  head  of 
the  meter  department,  or  his  assistant.  Any  abnormal 
increase  or  decrease  in  a  customer's  bill  should  be  investi- 
gated and  the  reason  for  the  same  found  out  if  possible, 
so  as  to  avoid  clerical  errors.  The  meters  in  circuit 
should  be  tested  periodically  and  a  record  kept  of  the  test, 
the  card  system  being  the  usual  form  of  record.  Various 
forms  of  cards  are  used,  but  the  one  shown  in  Fig.  61  is 
both  useful  and  convenient.  Besides  keeping  the  record  of 
the  test  for  reference,  it  is  interesting  and  instructive  to 
record  in  a  day-book  the  gross  amount  saved  by  these 


REMARKS 

Net  Bill 

1 

! 

O 

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£ 

y 

•snoQ 

Consumption 

S 

1 

a 

t 

I 

1 

j 

1 

1 

| 

S 

NAMES  AND  ADDRESS 

it 

a 

i 

o 


0 

1 


5 

B  z 


FIG.  60. 


RECORDS. 


131 


tests.  Simply  the  customer's  name  is  written,  and  in 
separate  columns  the  average  per  cent,  fast  or  slow  of  his 
meter  with  what  this  means  in  dollars  and  cents  taken  on 
the  basis  of  his  last  bill  is  noted. 

At  the  end  of  each  month  the  amount  saved  by  these 
tests  for  one  month  is  found  by  subtracting  columns  fast 
from  slow.  A  record  of  this  sort  demonstrates  clearly  the 
saving  that  is  effected  by  testing  the  meters,  and  from  it  an 
idea  is  obtained  of  how  often  it  pays  to  test  the  meters  in  a 


METER 
RECORD 


FIG.  61. 


consumer's   premises.     Further   discussion  will  be   found 
under  head  of  "Testing." 

The  filing  of  old  slips  and  cut-offs  must  be  done  in  such 
a  way  as  to  be  readily  accessible  when  needed.  The  alpha- 
betical system  furnishes  its  own  index  and  is  the  best  to 
follow.  Any  form  of  suitable  filing  case  will  do,  and  it  is  the 
practice  in  many  stations  to  file  all  documents  pertaining 
to  a  customer  in  one  envelope,  in  this  way  reducing  the  en- 


132  AMERICAN  METER  PRACTICE. 

tire  filing  system  to  one  cabinet.  Under  no  circumstances 
should  such  records  be  destroyed.  They  become  invalu- 
able in  the  event  of  a  law  suit.  There  are  many  minor 
records,  little  details  which  vary  with  local  conditions,  but 
the  value  of  keeping  in  writing,  easily  accessible,  every  com- 
munication pertaining  in  any  manner  to  the  work  cannot  be 
too  fully  emphasized.  We  pass  now  to  the  more  impor- 
tant part  of  the  work,  where  we  encounter  the  various 
problems  connected  with  the  correct  commercial  metering 
of  the  station's  output. 

This  part  of  the  work  is  the  golden  key  which  controls 
the  earning  power  of  the  plant.  It  may  be  divided  into 
four  branches:  Repairs,  Testing  in  the  meter  department, 
Testing  in  the  consumer's  premises,  General  Policy. 

The  repair  department  should  be  so  thoroughly  fitted  up 
as  to  render  unnecessary  the  sending  back  of  the  meter  to 
the  manufacturer  for  repairs.  A  thoroughly  competent 
electrical  mechanic  must  be  secured  who  is  capable  of 
making  all  repairs  of  every  character.  Besides  the  com- 
plement of  small  tools  used,  the  workshop  needs  one 
small  drill  press,  one  grinder  and  buffer,  one  lathe  head- 
stock.  The  electrical  instruments  needed  are  voltmeters 
according  to  the  variety  and  kind  of  service  used ;  a  portable 
testing  set  such  as  the  "Queen  Acme."* 

Meter  repairs  are  distinct  enough  in  character  for  us  to 
retain  the  division  between  the  inductive  and  non-inductive 
types.  The  repair  of  induction  meters,  having  a  closed 
metallic  secondary  for  an  armature,  is  simple.  Beginning 
with  the  armature  and  its'  shaft,  generally  the  only  repairs 
needed  will  be  a  new  shaft  end,  if  the  shaft  end  be 


*3ee  Kempster  B.  Miller's  "American  Telephone  Practice"   for 
full  description. 


OF  THE 

UNIVERSITY 

RECORDS- 


removable.  Except  in  case  of  mechanical  violence  metallic 
armatures  should  never  need  renewing.  The  potential  wind- 
ings of  an  induction  meter  are  liable  to  burn  out  as  are  also 
the  usual  impedance  coils  or  coil  in  series  therewith.  These 
coils  are  usually  form  wound,  and  can  be  obtained  from  the 
manufacturers  at  possibly  lower  cost  than  they  can  be 
wound  in  the  repair  shop.  Charts  of  the  proper  impedance 
of  the  different  sections  of  the  potentional  windings  can 
be  obtained  from  the  manufacturer.  The  known  resistances 
of  the  different  parts  of  the  potential  circuit  are  more  service- 
able than  their  impedances,  as  then  the  wheatstone  bridge 
can  be  used  to  verify  this  integrity  from  shunt  or  open  cir- 
cuit. When  the  resistance  is  known,  a  good  method  is  to 
connect  up  in  series  with  the  coil  to  be  tested  a  known 
resistance.  A  direct  current  passed  through  this  circuit 
should  give  falls  of  potential  across  each  coil  relative  to  the 
resistance  of  the  coils,  and  deviation  from  the  determined 
fall  of  potential  would  indicate  a  fault.  For  example,  we 
wish  to  test  an  impedance  coil  which  is  supposed  to  have 
400  ohms  resistance  in  series  with  this  coil.  We  place  a 
known  resistance  of  600  ohms  and  connect  up  to  a  100  v. 
direct  current  circuit.  If  the  400  ohm  coil  be  all  right  the 
fall  of  potential  across  it,  measured  by  a  volt  meter,  is  40 
volts;  if  partially  or  wholly  short-circuited  some  value 
under  40. 

In  replacing  defective  impedance  coils,  the  resistance  is 
relatively  of  least  importance.  The  exact  number  of  turns 
of  the  replaced  coil  must  be  present  in  the  new  one. 

The  series  field  coils  of  a  meter  are  frequently  burnt  out 
from  a  heavy  overload.  These  coils  can  be  wound  in  the 
repair  shop  or  bought  from  the  manufacturer.  As  a  gen- 
eral rule  it  is  found  preferable  to  buy  all  spare  parts  from 
the  manufacturer  and  simply  assemble  them  in  the  repair 


134  AMERICAN  METER  PRACTICE. 

shop.  The  greater  facilities  possessed  by  the  manufac- 
turer for  turning  out  the  various  parts  enable  him  to 
sell  at  a  profit  for  a  lower  price  than  it  costs  to  make  them 
specially. 

It  frequently  happens  that  the  magnetic  drag  on  alter- 
nating current  meters  loses  some  of  its  magnetism.  This  is 
due,  no  doubt,  to  the  almost  imperceptible  vibration  of  the 
meter  from  the  alternations  of  the  current.  New  magnets 
of  the  requisite  strength  should  replace  magnets  that  have 
lost  magnetism,  as  they  are  unreliable. 

The  three  main  matters  which  fill  almost  the  entire 
field  of  repairs  on  induction  meters  are  the  jewel  and  shaft 
end,  potential  circuit  and  field  coils. 

Let  us  follow  a  meter  through  its  different  stages  in  the 
repair  shop.  It  has  been  brought  in  from  the  circuit 
for  repairs.  Before  examining,  its  reading,  number, 
size,  etc.,  are  taken  and  recorded  in  a  day  book  which 
serves  as  a  running  record  of  the  daily  receipt  of  meters 
by  the  repair  shop.  The  cover  of  the  meter  is  removed, 
thoroughly  cleaned  and  repainted.  The  meter  is  then 
connected  in  circuit  and  a  load  put  on  it  to  see  whether  it 
is  electrically  or  mechanically  imperfect.  A  rough  test  of 
this  character  demonstrates  whether  the  potential  circuit 
is  intact,  and  a  glance  at  the  field  coils  will  tell  whether 
they  need  renewing.  If  these  parts  be  all  right  and  the 
meter  still  slow,  the  jewel  is  examined,  and,  if  cracked 
or  broken,  the  shaft  end  as  well  as  the  jewel  is  renewed. 
If  the  meter  has  no  jewel  or  shaft  end,  the  friction  must  be 
looked  for  in  the  guide  journal  of  the  armature  shaft. 
After  the  rough  test,  the  meter  is  taken  apart  and  cleaned 
thoroughly,  particular  attention  being  paid  to  the  moving 
parts.  After  re-assembling,  it  is  tested  roughly  for  accuracy 
and  grounded  frame.  It  is  then  ready  for  the  final  test 


RECORDS.  135 

in  the  calibrating  room,  the  features  of  which  will  be  gone 
into  later.  This  general  plan  is  followed  with  each  meter, 
no  matter  whether  cut  off  for  repairs  or  simply  discon- 
nected from  service.  The  mechanical  defects  in  the  running 
of  a  meter  are  easily  traced.  They  necessarily  lie  in  either 
or  both  bearings  of  the  armature  shaft,  in  the  dial  train  or  the 
clearance  either  of  the  armature  or  the  retarding  disk. 
The  remedy  in  any  case  is  easily  applied,  and  presents  no 
difficulty.  Taken  for  granted  that  the  meter  is  theoretically 
designed  properly,  the  electrical  defects  have  mainly  to  do 
with  the  continuity  or  insulation  of  the  different  circuits. 
If  both  be  intact,  no  repairs  are  necessary  in  this 
quarter. 

In  considering  the  repairs  of  non-inductive  meters,  we 
will  confine  ourselves  to  the  motor  type  and  take  as  an 
example  the  Thomson  wattmeter. 

The  repairs  to  this  meter  are  varied  in  character  owing 
to  its  having  an  armature  composed  of  wire  wound  in  coils 
and  a  commutator  and  brushes.  The  same  general  course, 
however,  is  pursued  that  has  already  been  outlined. 
Mechanical  defects  which  may  influence  the  accuracy 
of  the  meter  are  the  same  as  in  the  induction  meter,  and 
need  not  be  further  enumerated. 

After  the  meter  is  connected  in  circuit,  if  it  runs  at  all,  a 
voltmeter  is  connected  across  the  terminals  of  the  brush 
holders,  and  the  fall  of  potential  across  the  armature  coils 
obtained.  This  fall  of  potential  varies  with  different 
types  of  meters,  but  should  remain  constant  through  one 
revolution  or  armature.  If  this  fall  of  potential  vary 
more  than  two  volts  in  the  different  sections,  it  indicates  a 
defect  in  the  armature,  and  if  as  high  as  five  volts,  the 
meter  can — on  light  loads — be  seen  to  slow  up  when  the 
defective  section  is  reached.  Armatures  which  are  found 


136  AMERICAN  METER  PRACTICE. 

defective  must  be  replaced  by  new  ones,  as  it  does  not  pay 
to  find  the  defective  section  and  re-wind  it.  To  replace 
the  armature  the  leads  are  unsoldered  from  the  commu- 
tator, the  set-screws  holding  the  armature  body  to  the  shaft 
loosened,  and  the  old  armature  slipped  off.  The  new 
armature  is  put  on,  its  leads  soldered  and  the  commutator 
given  a  lead  of  about  90  degrees  from  armature  coils.  Be- 
fore placing  the  new  armature  in  the  meter  it  is  well  to  test 
it  in  an  improvised  circuit,  corresponding  to  the  potential 
circuit  of  the  meter.  A  set  of  brushes  is  so  arranged  that 
the  commutator  is  revolved  under  them  in  the  same 
manner  as  in  the  meter.  A  voltmeter  connected  as 
before  indicates  whether  the  new  armature  is  all  right. 
The  question  of  re-winding  armatures  in  the  repair 
shop  is  worth  considering  where  a  large  number  of 
Thomson  meters  are  used,  and  the  armature  renewals, 
heavy.  A  regular  armature  winding  machine,  such  as 
is  used  in  the  factory,  can  be  purchased,  or  one  may  be 
improvised  to  answer  the  purpose.  The  winding  is  simple,, 
the  sections  following  each  other  in  regular  rotation  and 
the  loops  brought  out  for  each  coil.  It  is  nice,  delicate 
work  and  can  be  done  advantageously  by  girls.  As  many  as, 
eight  to  ten  armatures  can  be  turned  out  by  one  girl  in  a 
day,  so  that  the  cost  of  labor  is  very  small.  In  small 
departments  it  would  not  pay  to  go  into  this  kind  of  work,, 
and  it  would  be  found  cheaper  to  throw  the  old  armature 
away  without  re-winding  it.  The  commutator,  if  scarred 
or  very  dirty,  should  be  polished  with  a  fine  piece  of  crocus 
cloth  and  then  blown  out  with  a  strong  blast  from  a  bellows 
to  remove  all  silver  particles  that  may  have  lodged  be- 
tween the  commutator  bars.  An  extra  polish  is  put  on  by 
finishing  with  a  piece  of  legal  tape,  and  in  almost  all  cases  a 
piece  of  legal  tape  is  all  that  is  needed.  The  brushes  are 


RECORDS.  .  137 

cleaned  by  removing  the  brush  holder  and  resting  the 
brush  against  a  firm  surface  and  then  polishing  with  a 
piece  of  crocus  cloth  pasted  on  a  stick.  After  the  brush- 
holder  is  replaced,  if  the  commutator  have  a  tendency 
to  spark,  hold  the  brushes  tightly  against  the  com- 
mutator with  two  fingers  and  revolve  the  shaft  with 
the  other  hand,  the  result  is  the  freeing  of  both  commutator 
and  brushes  of  any  roughness  or  foreign  particles.  The 
brush  tension  of  the  meter  is  of  much  importance.  It 
should  be  strong  enough  to  hold  the  brush  on  sufficiently 
hard  to  make  good  contact  and  not  to  fly  off  under  slight 
vibration,  causing  arcing.  Anything  which  causes  arcing 
at  the  brushes  is  disastrous  to  the  accuracy  of  the  meter. 
If  the  tension  is  made  too  strong  it  is  difficult  to  make  the 
meter  run  correctly  on  light  loads  without  increasing  the 
starting  coil.  There  is  found  by  experiment  just  the 
right  tension  for  the  best  results  and  the  tension  is  ascer- 
tained by  the  "feel"  of  the  brush  when  drawn  away  from 
the  commutator.  The  resistance  of  the  coil  at  the  back 
of  the  meter  in  series  with  the  armature  is  usually  marked 
on  it,  and  if  this  coil  is  burnt  out  it  is  replaced  with  one  of 
the  same  number  of  ohms.  The  starting  coil  may  be  also 
frurnt  out  and  both  starting  coil  and  resistance  may  be 
wound  to  advantage  in  the  repair  shop.  In  rewinding 
the  starting  coils  the  same  number  of  turns  must  be  put  on. 
When  the  integrity  of  the  potential  circuit  is  established  in 
every  part,  the  jewel  and  shaft  end  being  in  perfect  con- 
dition, and  the  copper  disk  and  armature  having  the  proper 
clearance ,  the  meter  should  be  approximately  correct.  After 
the  test  in  the  repair  room,  it  is  turned  over  to  the  testing 
room  for  calibration.  In  changing  a  meter  from  a  low 
efficiency  to  the  high  efficiency  type,  the  alteration  is  con- 
fined to  the  potential  circuit.  In  fact,  the  entire  potential 


138  AMERICAN  METER  PRACTICE. 

circuit  is  changed,  a  new  armature,  resistance  and  start- 
ing coil  being  put  in.  The  fields,  frame  and  magnetic 
drag  remain  the  same. 

The  change  results  in  an  increased  efficiency  of  the 
meter  on  light  loads  with  a  decreased  consumption  of 
energy  in  the  potential  circuit.  The  advantages  of  this 
change  make  it  highly  desirable  and  all  the  low  efficiency 
meters  can  be  gradually  changed  to  high  efficiency  with- 
out prohibitive  cost.  In  changing  over  meters  from  50 
volts  to  100  volts,  two  courses  are  open,  the  one  to  wind  an 
increased  resistance  until  the  ampere  flow  in  the  potential 
circuit  is  the  equivalent  of  what  it  was  at  50  volts.  This 
makes  a  meter  of  low  efficiency  with  double  the  capacity 
of  lights  at  100  volts.  The  other  course  is  to  change  the 
armature  resistance  and  starting  coil  to  similar  high 
efficiency  100  volt  parts.  In  either  case  the  capacity  of 
the  meter  is  double  that  of  50  volts,  and  at  the  same  con- 
stant as  the  regular  type  100  voltmeter  of  the  same  size. 
An  exception,  however,  is  the  ten  ampere  50  voltmeter, 
which  also  has  its  magnetic  drag  halved  to  bring  it  to 
constant  one-half.  The  same  general  policy  is  pursued  in 
changing  to  any  voltage.  Meters  are  tested  to  ascertain 
whether  they  will  register  a  given  load  for  a  given  time 
accurately.  In  other  words,  the  energy  passing  through 
the  meter  must  make  the  meter  revolve  in  exact  pro- 
portion to  its  amounts.  Nearly  all  mechanical  meters 
make  one  revolution  of  the  armature  for  one  watt  hour, 
hence  we  derive  the  formula: 

No.  revolutions  X  constant  X  3600 

=  seconds  in  which 

watts 

the  meter  should  make  the  given  number  of  revolutions. 
To  count  the  number  of  revolutions  in  a  given  time  accu- 
rately a  stop  watch  is  used.  A  mark  is  made  on  the 


RECORDS. 


139 


revolving  disk,  and  a  meter  under  test  is  given  a  run  of  say 
20  revolutions.  The  exact  elapsed  time  is  caught  by  the 
stop  watch,  and  the  rate  at  which  energy  was  flowing 
through  the  meter  is  obtained  from  the  instruments  in 
circuit.  The  application  of  the  above  formula  will  de- 
termine whether  the  meter  is  fast  or  slow. 


FIG.  62. 

The  indicating  instruments  to  determine  the  amount  of 
energy  passing  in  the  circuit  are  connected  in  a  number  of 
ways.  In  Fig.  62  the  ammeter  and  voltmeter  are  connected 
before  the  meter,  hence  the  amount  of  current  used  by  the 
potential  circuit  is  registered  on  the  ammeter  and  fall  of 
potential  across  the  fields  of  the  meter  by  the  voltmeter. 


FIG.  63. 

If  the  meter  is  calibrated  on  this  basis,  the  consumer  pays 
for  the  current  used  in  the  potential  circuit  of  the  meter  as 
well  as  the  loss  in  the  fields.  The  usual  combined  losses  in 
the  meter  are  about  2  per  cent,  of  full  load  rating,  hence  in 
this  connection  the  consumer  would  pay  for  2  per  cent, 
more  energy  than  was  actually  delivered  to  him.  In 
Fig.  63,  where  the  ammeter  is  placed  after  the  meter,  the 


140 


AMERICAN  METER  PRACTICE. 


loss  in  the  potential  circuit  is  sustained  by  the  supplier 
of  current,  and  the  loss  in  the  fields  by  the  consumer. 
This  is  generally  the  accepted  plan  for  dividing  the  losses, 
and  is  fairer  to  the  consumer  than  the  other  method. 
In  Fig.  56  the  ammeter  and  voltmeter  are  both  connected 
after  the  meter,  and  the  central  station  bears  both  field 
and  potential  circuit  losses.  We  have  pointed  out  in 
previous  chapters  that  the  average  loss  in  meters  was  15 
per  cent,  of  the  total  amount  of  current  supplied.  This 
being  the  case,  the  connection  for  calibration  shown  in 
Fig.  64  will  help  to  eliminate  this  loss  by  2  per  cent.,  and 
should  always  be  used  for  this  reason  in  calibrating  meters 
for  service.  Care  should  be  exercised  in  connecting  the 


FIG.  64. 

voltmeter  that  its  current  is  not  registered  by  the  am- 
meter. Connections  for  three-wire  meters  are  modifica- 
tions of  the  above.  It  is  assumed  that  the  current  to  be 
measured  is  non-inductive.  If  an  indicating  wattmeter 
replace  the  volt  and  ammeter,  the  series  coils  of  the  watt- 
meter take  the  place  of  the  ammeter  and  the  potential  coils 
that  of  the  voltmeter. 

TESTING  IN  METER  DEPARTMENT. 

The  outfit  for  calibrating  meters  in  different  stations 
varies  with  the  degree  of  importance  attached  to  this 
branch  of  the  work.  It  is  needless  to  emphasize  the  fact 
that  a  correct  calibration  of  the  meters  before  they  are 
installed  is  of  the  utmost  importance. 


TESTING.  141 

The  instruments  necessary  for  the  work  vary  with  the 
class  and  size  of  the  meters  to  be  tested  and  'naturally 
divide  themselves  into  two  classes,  direct  and  alternating. 
Direct  current  testing  will  be  considered  first.  The  usual 
commercial  circuits  are  distributed  at  no,  220  and  500 
volts  potential. 

To  measure  the  energy  passing  in  a  direct  current  circuit 
by  means  of  an  indicating  wattmeter  it  is  necessary  to  take 
reversed  readings,  the  mean  of  which  is  the  true  reading. 
It  is  found  quicker  to  use  a  volt  and  ammeter  and  obtain 
the  product  of  the  readings.  If  a  station  is  distributing 
three  direct  potentials  no,  220  and  500,  two  standard  volt- 
meters are  needed,  one  with  double  scale  reading  from  o  to 
150  and  o  to  300,  the  other  for  500  voltsreading  from  250 
to  600  volts.  The  number  of  ammeters  can  be  limited  to 
two,  one  double  scale  instrument  reading  from  o  to  10  and 
oto5oini-io  amperes  and  J  amperes  divided  respectively, 
and  another  instrument  reading  from  o  to  500  amperes  for 
heavy  work. 

These  instruments  should  be  of  standard  dead  beat  type 
and  extremely  accurate.  The  accuracy  of  all  the  instru- 
ments used  in  testing  should  be  checked  once  a  week,  and 
oftener  if  inaccuracy  is  suspected. 

The  design  and  requirements  of  the  testing  board  vary 
with  the  number  of  meters  tested  per  day,  but  for  any 
capacity  the  board  should  be  laid  out  in  such  a  way  as  to 
enable  testing  to  be  done  as  quickly  as  possible.  Before  going 
into  the  arrangements  of  switches  and  instruments  a  brief 
discussion  of  the  kind  of  current  to  be  used  in  testing  is  in 
order.  If  the  station  is  provided  with  a  storage  battery, 
leads  direct  from  the  battery  should  supply  the  testing 
fcoard,  so  as  to  avoid  the  fluctuation  of  the  voltage  on  the 
lines.  It  is  customary  to  charge  station  batteries  at  night 


142 


AMERICAN  METER  PRACTICE. 


from  about  12  P.  M.  to  7  A.  M.  and  let  them  "  float  "  on  the 
lines  in  the  day  time.  The  leads  to  the  testing  board 
would  be  at  practically  the  same  voltage  all  day.  In 
event  of  no  battery  being  installed,  leads  direct  from  the 
bus  bars  of  the  plant  would  furnish  a  steadier  current  than 
the  lines,  and  the  voltage  could  be  reduced  by  inserting  a 
resistance  in  series  with  the  circuit.  Leads  from  the  service 
mains  are  the  least  to  be  desired,  owing  to  the  fluctuation 


Gen.  3  volts 


Motor  120  volts 
FIG.  65. 


Gen.  50  voll 


caused  by  varying  motor  loads.  In  a  well-laid-out  system 
the  fluctuation  is  small,  but  can  easily  be  3  per  cent, 
either  way  and  is  a  source  of  error  because  it  necessitates 
guessing  at  an  average  value. 

A  testing  system  which  is  by  far  superior  to  either  of 
these  three  is  obtained  by  installing  a  small  storage  battery 
of  sufficient  number  of  cells  to  furnish  a  three-wire  service 
of  100  to  220  volts.  These  cells  can  be  quite  small, 


TESTING. 

either  of  7  or  10  ampere-hour  capacity,  as  they  furnish 
current  only  for  the  potential  circuits  of  the  meter.  The 
use  of  this  battery  in  photometer  work  is  described  in 
Chapter  XVI. 

The  load  on  the  series  coils  of  the  meter  is  furnished  by 
either  one  or  two  large  cells  in  series  of  about  600  ampere- 
hour  capacity,  and  a  normal  discharge  rate  of  75  amperes. 
The  short  circuit  value  of  two  of  the  cells  in  series  would  be 
about  300  to  400  amperes.  These  batteries  are  connected 
in  series  with  the  field  coils  of  the  meter  through  a  variable 
resistance.  The  connections  for  the  charging  set,  switch- 
board and  batteries  are  shown  in  Fig.  65. 

For  storing  purposes,  this  small  motor,  driving  the  low 
voltage  generator  for  the  large  cells  and  the  booster  in 
series  with  the  line  current  for  the  small  cells,  gives  a  very 
neat  and  effective  outfit. 

The  motor  is  mounted  in  between  the  booster  and  gen- 
erator on  one  bed  plate  and  is  directly  coupled  to  each. 

The  meter  testing  board  if  laid  out  for  use  with  line  cur- 
rent must  employ  either  lamp  banks  or  rheostats  capable 
of  dissipating  large  amounts  of  energy.  The  system  just 
described  uses  only  about  one-fiftieth  of  the  energy  con- 
sumed by  the  other  method.  The  variable  resistance 
placed  in  circuit  with  the  field  coils  of  the  meter  gives  any 
desired  load  without  in  any  way  affecting  the  voltage  of  the 
potential  circuit. 

Five-hundred-volt  meters  can  be  tested  on  this  battery 
system  by  obtaining  the  fall  of  potential  across  the  arma- 
ture and  starting  coil  and  applying  this  voltage  from  the 
batteries  across  this  circuit,  the  field,  as  in  the  other  low 
voltage  meters,  being  in  series  with  the  low  voltage  circuit 
from  the  large  batteries.  In  effect  this  test  gives  the 
same  result  as  though  500  volts  were  used. 


144 


AMERICAN  METER  PRACTICE. 


Before  laying  out  the  testing  board,  it  must  be  decided  by 
what  current  the  meters  are  to  be  tested ,  as  great  simplifi- 
cation results  in  using  the  battery  system. 

For  small  stations  the  expense  of  a  battery  outfit  would 
hardly  be  justified,  and,  for  this  reason,  a  complete  testing 


OuQuudS 


FIG.  66.       B 

board  employing  one  lamp  bank  for  the  three  voltages  will 
be  given  as  well  as  a  diagram  of  connections  for  battery 
system. 

In  Fig.  66,  we  have  a  three-wire  no  to  220  volt  service 
and    a    500    volt,    no    volt    A.  C.  and    D.  C.    two-wire 


TESTING.  145 

service  feeding  a  common  three-wire  bus  C.  From  C  are 
let  three  sets  of  three-wire  leads  to  a  triple  row  of  binding 
posts  at  D,  E  and  F.  The  upper  rows  of  these  binding 
posts  feed  into  bus  bar  G.  Single  pole  switches  are  in- 
serted in  leads  from  C  to  lower  row  of  binding  posts. 
The  bus  bar  G  feeds  ten  rows  of  lamps  which  are  con- 
nected up  as  shown  in  diagram,  five  on  each  side  of  the 
system.  The  meter  to  be  tested  is  fed  from  lower  row 
of  binding  posts  at  either  D,  E  or  F,  and  the  return 
leads  connected  to  top  row  feeding  lamp  banks.  Each 
row  of  lamps  is  provided  with  single  pole  switches  on  each 
leg,  and  a  tie  over  switch  at  H  enables  both  sides  of  the 
lamp  bank  to  be  used  on  either  side  of  the  system.  The 
rows  of  lamps  are  fed  in  such  manner  that  the  wires  of 
adjacent  rows  are  of  the  same  potential  and  are  perma- 
nently tapped  together.  The  right  hand  part  of  the  bank  is 
subdivided  by  breaking  the  rows  of  lamps  above  the 
second  lamp  by  means  of  a  row  of  single  pole  switches. 

The  great  flexibility  of  this  arrangement  is  apparent,  as 
a  two  or  three-wire  meter  can  be  tested  from  a  load  of  one 
lamp  up  to  entire  load  of  lamp  bank. 

In  testing  on  500  volts,  all  switches  are  opened  except 
those  at  the  ends  of  each  five  rows.  The  current  then 
flows  in  series  with  five  lamps  in  multiple  and  up  to 
the  full  capacity  of  the  bank.  This  form  of  lamp 
bank  is  very  convenient  in  operation  and  is  cheaper 
in  first  cost  than  two  distinct  banks  for  low  and  high 
voltage. 

The  lamps  are  arranged  on  the  back  of  the  board  so  as 
to  shield  the  operator's  eyes  from  the  glare  and  heat.  The 
most  convenient  arrangement  is  to  have  the  lamps,  switches, 
etc.,  mounted  on  a  slate  or  marble  panel,  set  at  the  rear 
«dge  of  the  meter  testing  table. 


146  AMERICAN  METER  PRACTICE. 

Fig.  67  gives  diagrammatically  the  connections  used  with 
the  large  and  small  storage  batteries.  A  is  field  battery, 
B  potential  batteries,  C  variable  resistance  in  series  with 
field  battery,  D  regular  type  Thomson  meter. 

As  shown  the  connections  are  very  simple,  and  need  only 
be  modified  for  testing  three-wire  meters  by  placing  both 
fields  of  the  meter  in  series.  It  is  customary,  where  a 
large  number  of  meters  are  tested  daily,  to  connect  up  a 
number  of  them  in  series  with  each  other  and  a  carefully 
calibrated  standard  meter  of  the  same  type.  This  method 
is  possibly  quicker  than  testing  each  meter  individually,  but 
is  liable  to  several  errors  which  may  be  overlooked  by  some. 


FIG.  C7. 

When  the  meters  are  connected  in  series,  the  fall  of 
potential  across  the  fields  of  the  meter  diminishes  the 
potential  delivered  to  the  next  meter  by  that  amount, 
hence  the  potential  circuit  of  the  succeeding  meter  operates 
at  a  lower  voltage  than  its  predecessor;  in  fact,  it  will  regis- 
ter less  by  the  exact  amount  of  PR  losses  in  the  fields  of  the 
preceding  meter.  The  current  consumed  in  the  potential 
circuit  of  the  succeeding  meter  is  registered  on  the  pre- 
ceding one,  so,  as  we  descend  down  the  line,  each  meter 
registers  less  than  its  predecessor  by  the  watt  losses  of  the 
former.  If  the  watt  losses  at  full  load  be  10  watts,  and 


TESTING.  147 

10  meters  were  in  series,  the  first  meter  would  register  100 
watts  more  than  the  last  one.  As  the  load  is  varied  this 
percentage  varies  as  the  I*R  losses  in  the  fields  vary,  so 
that,  in  order  to  get  a  correct  register,  the  potential  cir- 
cuits of  each  meter  must  be  fed  separately  from  the  field 
circuit.  This  involves  disconnecting  the  potential  circuits 
and  feeding  them  separately,  which  is  troublesome.  In 
the  battery  systems,  where  the  potential  and  field  cir- 
cuits are  independent  in  origin,  no  such  trouble  exists. 
The  potential  circuits  need  not  be  disconnected,  as  they  are 
fed  independently  by  the  high  voltage  battery  circuit,  which 
has  its  positive  voltage  connected  to  positive  of  low  voltage 
circuit  in  the  meter.  The  individual  adjustment  of  a  meter 
takes  as  long,  whether  it  be  connected  in  series  with  many 
others  or  by  itself;  and,  as  each  meter  has  to  receive  its  in- 
dividual adjustment,  it  is  no  gain  in  this  respect  to  connect 
it  in  series.  Meters  require  a  heat-run  of  from  20  minutes 
to  a  half  hour  to  allow  the  resistances  of  the  potential  and 
field  circuit  to  assume  their  normal  conditions.  For  this 
reason,  it  is  a  gain  to  have  a  number  of  meters  connected  in 
circuit  ready  to  receive  their  individual  calibration.  The 
use  of  the  battery  system  enables  meters  to  be  adjusted 
with  great  speed  and  accuracy.  The  variable  resistance  in 
series  with  the  fields  is  adjusted  to  allow  a  fixed  number  of 
amperes  to  flow.  The  voltage  of  the  potential  circuit  is 
constant  and  is  not  subject  to  varying  field  strength,  as  the 
circuits  are  independent  in  origin.  For  any  given  ampere 
value  the  watts  are  known  and  will  always  be  exactly  the 
same  for  this  value;  hence,  to  test  the  meter,  a  series  of 
ampere  values  are  taken  and  the  meter  speed  noted  and 
adjusted.  It  does  not  become  necessary  to  make  frequent 
calculations  of  energy  value  because  it  is  always  constant, 
the  only  variable  being  the  load,  and  that  is  made  whatever 


148  AMERICAN  METER  PRACTICE. 

one  chooses.  In  employing  only  one  source  of  energy,  a 
varying  field  strength  gives  a  varying  voltage  owing  to  the 
drop  in  the  leads  and  field  coils,  and  a  new  calculation  has 
to  be  made  for  each  change  of  field  strength. 

To  sum  up,  it  appears  that  the  battery  system  has  a 
number  of  advantages  over  any  other,  whether  the  meters 
are  tested  individually  or  in  series. 

Alternating  current  meter  testing,  where  a  central 
station  employs  Thomson  meters  for  both  direct  and  alter- 
nating current,  may  be  carried  out  altogether  on  the  direct 
current  testing  board,  as  the  calibration  is  practically  the 
same  for  either  alternating  or  direct  current. 

For  induction  meters  we  employ  lamp  banks,  rheostats  or 
motors  to  furnish  a  load  for  the  meter.  If  the  load  is 
purely  non-inductive,  an  ampere  and  voltmeter  can  be 
used  to  measure  the  energy  input,  but,  as  the  load  may  be 
frequently  inductive,  it  is  best  to  fit  up  the  testing  board 
with  indicating  wattmeters.  In  connecting  up  the  meters 
for  various  kinds  of  service,  the  instructions  given  in 
Chapter  II  must  be  followed  in  determining  the  true  watt 
input  flowing  through  the  meter.  In  other  respects  the 
same  general  rules  are  followed  as  given  for  direct  current 
meter  testing. 

TESTING  IN  CONSUMER'S  PREMISES. 

The  test  of  a  meter  in  the  consumer's  premises  is  made 
for  either  of  two  reasons :  a  complaint  by  the  consumer  of 
high  bills,  or  to  check  the  accuracy  of  the  meter  for  the 
benefit  of  the  central  station.  For  whatever  cause,  this 
test  is  made  in  several  ways.  The  merits  of  all  will  be  con- 
sidered. The  meter  may  be  tested  by  volt  and  ammeter, 
indicating  wattmeter,  calibrated  lamp  bank  or  standard 
recording  meter  in  series  with  the  meter  to  be  tested.  In 


TESTING.  149 

testing  with  volt  and  ammeter  an  approximation  may  be 
reached,  but  the  method  is  open  to  various  objections. 
The  fluctuation  of  voltage  on  the  lines,  and  the  fluctuation  of 
the  load  in  the  premises,  make  it  impossible  in  many  in- 
stances to  obtain  more  than  an  approximate  test.  Es- 
pecially is  this  the  case  where  the  load  is  a  motor  running 
a  shop  or  direct  connected  elevator.  The  man  making  the 
test  has  four  moving  objects  to  attend  to  at  one  time,  am- 
meter, voltmeter,  stop  watch  and  moving  meter  disk,  and 
the  consequence  is  that  he  can  never  be  sure  that  the  test 
is  a  correct  one.  On  alternating  current  lines,  where  the 
load  is  inductive,  it  is  not  possible  to  get  a  correct  test  by 
this  method  unless  the  exact  power  factor  of  the  circuit 
passing  through  the  meter  is  determined.  In  practice  this 
is  not  feasible  so  the  above  method  is  never  used.  An  in- 
dicating wattmeter  may  be  used  instead  of  the  volt  and 
ammeter,  and  has  the  advantage  of  reducing  the  number 
of  objects  to  be  watched  by  one.  On  alternating  circuits, 
where  the  load  is  inductive,  the  indicating  wattmeter  is 
very  much  used  and  is  the  proper  thing  in  testing  where  the 
load  is  not  subject  to  variation. 

The  third  method,  a  calibrated  lamp  bank,  necessitates 
the  shunting  of  the  service  and  disconnecting  the  meter 
from  its  load.  The  lamp  bank  is  composed  of  lamps  of 
known  wattage  at  known  voltages,  and  the  only  instrument 
needed  is  a  voltmeter.  The  lamp  bank  is  connected  to  the 
meter,  and  furnishes  a  load  with  which  to  test  it.  If  the 
voltage  on  the  lines  is  variable,  as  is  likely  to  be  the  case 
where  a  heavy  day  motor  load  is  connected  to  the  system, 
the  wattage  of  the  calibrated  lamp  bank  has  to  be  averaged 
in  the  same  manner  that  the  indicated  watt  readings  were ; 
there  is,  however,  this  advantage,  that  the  load  is  steady. 
In  large  installations,  where  the  meter  would  need  at  least 


150 


AMERICAN  METER  PRACTICE. 


the  equivalent  of  100— i6's  connected  for  a  test,  the  lamp 
bank  method  is  too  cumbersome  to  lend  itself  readily  to 
economical  transportation  from  house  to  house.  One  of 
the  gravest  objections  to  this  method  of  testing  is  the  time 
and  trouble  taken  in  shunting  the  wiring  of  a  large  installa- 


FIG.  68. 

tion,  otherwise  the  consumer  is  cut  out  of  light  for  a  half 
hour  or  more. 

The  fourth  method,  the  placing  of  a  standard  recording 
wattmeter  in  series  with  the  meter  in  the  premises,  permits 
of  an  accurate  test  to  be  made  under  any  variation  of  load 


TESTING.  151 

and  voltage.  The  standard  portable  meter  is  easily  rigged 
up  from  the  usual  stock  type  by  attaching  chains  with 
turnbuckles  to  the  frame  of  the  meter,  in  such  a  way  as  to 
allow  the  standard  meter  to  be  suspended  from  the  one  to  be 
tested  by  means  of  hooks.  To  properly  hang  the  meter 
four  points  are  selected  on  the  frame,  and  chains  connected. 
These  lead  to  a  hook  on  each  side  of  the  meter  which  is  used 
to  hang  the  meter  from  the  one  to  be  tested.  A  diagram- 
matic representation  is  shown.  Fig.  68  shows  connection  of 
chain  and  a  view  of  the  portable  meter  as  it  would  appear 
when  suspended  from  the  one  to  be  tested.  The  meters  are 
then  placed  in  series,  and  the  load  in  the  premises  applied. 
The  meter  disks  are  held  in  the  same  relative  position  with 
reference  to  a  mark  on  them  and  allowed  to  start  at  the 
same  time.  After  one  or  two  revolutions  it  becomes 
apparent  whether  the  meter  to  be  tested  is  fast  or  slow  by 
the  relative  position  of  the  marks  on  the  disks.  If  slow, 
the  meter  being  tested  is  cleaned,  the  jewel  examined  and, 
if  defective,  is  replaced  by  new  jewel  and  shaft  end,  if  the 
parts  are  accessible.  Another  trial  will  show  the  effect 
of  these  operations,  and,  if  still  slow,  an  adjustment  of  the 
magnets  acting  as  a  drag  can  be  made  until  the  meters  run 
in  unison.  While  this  test  is  being  made  the  operation  is 
entirely  independent  of  any  variation  in  voltage  or 
load  as  both  meters  are  affected  alike  by  any  change  in 
either. 

On  direct  connected  elevators  and  motors  of  all  sorts, 
this  method  is  the  only  one  which  will  allow  of  a  correct  test 
being  made  on  the  meter  with  the  load  which  it  has  to 
carry. 

The  ratio  of  the  energy  passing  through  the  standard 
and  tested  meters  varies  with  the  position  of  the  standard 
meter;  that  is,  whether  it  is  placed  before  or  after  the  one 


152  AMERICAN  METER  PRACTICE. 

to  be  tested.  If  before,  it  receives  more  energy  by  the 
watt  losses  of  the  tested  meter;  if  after,  less  energy  by  the 
watt  losses  of  the  tested  meter,  that  is,  assuming  both  meters 
to  be  of  the  same  capacity  and  efficiency. 

In  making  a  test  it  is  immaterial  whether  the  meters 
are  connected  before  or  after,  as  long  as  the  watt  losses  are 
added  or  subtracted  from  the  standard.  In  many  makes 
of  meters  the  watt  losses,  for  practical  purposes,  may  be 
neglected  in  making  a  test. 

To  make  the  matter  clearer,  suppose  the  consumer  has  a 
T.  H.  meter  of  five  ampere  capacity,  and  the  standard 
portable  meter  is  of  five  ampere  capacity.  If  the  standard 
meter  is  connected  in  front  of  the  meter  to  be  tested,  and 
the  watt  losses  of  the  two  meters  on  the  same  load  are 
equal,  then,  when  500  watts  are  delivered  to  the  consumer 
with  a  10  watt  loss  in  each  meter,  we  have  the  following: 

520  watts  delivered  to  service  side  of  standard  meter. 
4       "     loss  in  potential  circuit  " 
6       "       "    "  field  "        "         "  =I2R. 


510  delivered  to  meter  to  be  tested. 

Assuming  the  internal  losses  of  the  meters  to  be  unregis- 
tered, we  have  the  standard  meter  recording  510  watts  of 
energy  and  the  meter  to  be  tested  500  watts.  In  other 
words,  on  full  load  the  standard  would  run  one-half  of  i 
per  cent,  faster  than  the  meter  to  be  tested.  In  com- 
mercial tests  a  percentage  of  this  magnitude  may  be 
neglected,  but,  as  the  load  decreases,  the  percentage  of 
error  becomes  greater  as  the  PR  losses  in  the  fields  become 
less;  that  is,  on  a  load  of  50  watts  the  standard  meter  would 
receive  approximately  4.6  watts  more  energy  than  the 
meter  to  be  tested,  or  9  per  cent.  In  adjusting  a  meter,  it  is 
always  made  correct  on  full  load  first  and  then  its  efficiency 


TESTING.  153 

on  one  light  load  ascertained.  If  the  standard  meter  is  con- 
nected behind  or  after  the  meter  to  be  tested,  it  runs  slower 
than  the  one  to  be  tested,  and  this  is  bad  practice,  for  this 
reason.  If  the  consumer  is  watching  the  test  and  sees  his 
meter  slower  than  the  standard,  he  is  satisfied  that  the 
meter  is  performing  properly ;  if  his  meter,  on  the  contrary, 
runs  faster  than  the  standard,  no  amount  of  explanation 
will  satisfy  him.  Therefore,  it  is  good  practice  to  place  the 
standard  meter  always  in  front  of  the  meter  to  be  tested. 

If  the  test  is  being  conducted  for  the  consumer,  he  or  his 
representative  usually  watches  the  operation  and,  if  they 
possess  no  technical  knowledge  on  the  subject,  the  graphic 
method  of  placing  two  meters  in  series  appeals  to  them 
more  strongly  than  when  conducted  by  indicating  instru- 
ments of  which  they  know  nothing. 

Again,  when  instruments  are  used  a  stop  watch  is  nec- 
essary to  catch  the  number  of  revolutions  accurately,  so 
that  we  have  to  contend  with  the  personal  error  of  the 
observer  in  reading  the  indicating  meters  and  catching  the 
time.  It  is  impossible  for  one  man  to  do  this  correctly,  he 
cannot  watch  his  instruments  and  the  meter  at  the  same 
time.  Two  men  are  necessary,  and  the  expense  of  testing 
is  doubled.  The  series  method  needs  only  one  man,  no 
reading  or  calculations  are  necessary,  a  variable  load  or 
voltage  affects  both  meters  alike,  the  per  cent,  fast  or  slow 
may  be  ascertained  to  any  degree  of  accuracy  by  taking  a 
large  number  of  revolutions  for  comparison.  All  of  these 
advantages,  and  the  saving  in  expense,  place  this  method  far 
ahead  of  the  others. 

Meters  of  100  ampere  capacity  and  over,  owing  to  the 
large  wires  to  which  they  are  connected,  are  troublesome  to 
test  and  make  the  necessary  connections.  On  any  system 
the  number  of  such  meters  on  the  circuit  is  a  very  small 


154  AMERICAN  METER  PRACTICE. 

percentage  of  the  whole,  and  it  has  been  found  by  expe- 
rience that  the  quickest  and  cheapest  way  to  test  these 
meters  is  to  remove  them  altogether  and  replace  them  by 
new  ones.  Suppose  in  a  system  of  5,000  meters,  50  of 
them  were  100  ampere  capacity  and  over.  To  test  these 
meters  once  a  year  it  would  be  necessary  to  change 
four  of  them  each  month;  that  is,  a  reserve  of  four  or 
five  meters  of  different  sizes  would  enable  all  these  meters 
to  be  brought  back,  tested  and  sent  out  again. 

The  sizes  of  portable  meters,  then,  to  be  carried  in  stock 
are  few  in  number,  say  five  or  six.  These  meters  are  care- 
fully calibrated  before  being  put  in  service  and  are  checked 
before  and  after  each  day's  work.  Their  calibration,  with 
proper  handling,  remaining  remarkably  constant.  The 
jewel  screw  is  always  kept  lowered  and  the  disk  firmly 
wedged  when  not  in  use. 

On  a  large  system  of  meters,  where  two  or  more  meter 
testers  are  employed,  the  work  is  so  arranged  that  each  man 
tests  only  one  size  of  meter  during  a  day.  The  tester 
follows  the  regular  meter  routes,  and  on  one  day  tests  one 
size  of  meter  and  the  next  another  and  so  on,  so  that  the 
number  of  portable  meters  even  for  a  large  system  may  be 
kept  down  to  one  meter  for  each  size. 

The  desirability  of  regular  meter  testing  has  been  proved 
so  conclusively  that  it  need  not  be  gone  into,  but  the 
question  of  how  often  to  test  is  one  which  varies  with  local 
conditions  and  the  kind  of  meter  used.  As  a  general  con- 
dition twice  a  year  is  about  right,  but  in  localities  where  the 
meters  are  subject  to  vibration  from  heavy  traffic  more  fre- 
quent tests  result  in  very  material  saving  in  the  meter  bills. 

If  a  list  of  the  tests  made  and  the  amounts  saved  be 
kept,  such  a  record  enables  the  question  of  how  often  it 
pays  to  test  to  be  settled  beyond  dispute. 


GENERAL  POLICY.  155 

The  General  Policy  of  the  meter  department  should  have 
two  ends  in  view,  the  giving  of  as  perfect  meter  service  as 
it  is  possible  to  establish,  and  the  maintaining  of  harmo- 
nious relations  with  the  consumer.  Some  natural  divisions 
suggest  themselves,  such  as: 

1.  Should  central  stations  make  meter  tests  without 
charge  ? 

2.  The  education  of  the  Consumer. 

3.  Duties  of  the  Meter  Readers. 

4.  Cleaning  meters. 

5.  Jewel  renewals. 

1 .  It  has  been  found  by  experience  that  bills  complained 
of  are  much  more  easily  settled  after  a  test  of  the  meter  has 
been  made.     This  test  furnished  to  the  adjuster  enables 
him  to  know  definitely  whether  the  meter  is  fast  or  slow  and 
facilitates  a  settlement  in  that  way.     From  the  viewpoint 
of  cost  to  the  central  station  it  averages  about  50  cents  to 
test  a  meter  in  the  premises,  and,  as  the  meters  as  a  rule  are 
slow,  the  adjusting  of  the  meter  to  run  correctly  more  than 
compensates  for  the  cost  of  the  test.     As  an  economic 
practice,  the  testing  of  meters  for  consumers  is  desirable, 
and  under  no  circumstances  should  they  be  discouraged 
by  charging  for  the  test.     The  writer  has  had  occasion  to 
change  his  views  on  this  point  within  the  past  two  years 
since  collecting  data  on  the.  subject,  which  data  showed 
conclusively  that  the  central  station  saves  many  times 
over    the  cost    of    testing   by    adjusting    the    meters  to 
run    correctly.      The    manner    in    which    the    record  is 
kept  is   detailed    more    fully    under    "Records"   in  this 
chapter. 

2.  The  widely  extended  use  to  which  electricity  is  put 
in  every  branch  of  life  is  gradually  lessening  the  general 


156  AMERICAN  METER  PRACTICE. 

ignorance  of  the  public  on  electrical  sub j  ect s .  The  ma j  orit 7 
are  still  wrapped  in  profound  ignorance  of  the  simplest 
fundamentals,  and  the  meter  to  such  people  is  a  wholly 
mysterious,  eccentric  and  untrustworthy  piece  of  apparatus. 

It  would  be  a  useless  effort  to  try  to  educate  the  con- 
sumer in  the  principles  upon  which  his  meter  operates, 
but  he  should  have  a  knowledge  of  the  manner  in  which  his 
bill  is  determined.  Many  of  them  can  read  the  dials  cor- 
rectly, but  cannot  figure  out  the  bill  from  the  readings. 
An  excellent  method  of  placing  in  each  consumer's  hands 
the  knowledge  of  how  to  arrive  at  his  bills  is  to  get  up  an 
instruction  card,  showing  a  dial  with  a  sample  reading 
thereon  and  go  through  the  process  of  getting  the  bill. 
This  card  can  be  mailed  to  each  consumer  or  left  by  the 
meter  readers,  and,  as  a  result,  the  consumer's  curiosity  is 
excited  to  know  the  amount  of  his  bill,  and  he  tests  his 
meter  by  the  dial  to  find  out  whether  it  is  correct.  The 
better  he  comes  to  know  the  meter,  the  more  respect  he 
has  for  its  correctness,  and  fewer  complaints  are  turned  in 
of  "high  charges."  If  we  could  conceive  of  the  condition 
of  every  consumer  being  able  to  read  and  test  his  meter, 
the  complaint  adjuster  would  have  very  little  to  do,  as  then 
only  the  real  errors  would  be  brought  in. 

The  results  from  distributing  the  instruction  cards  have 
been  found  very  beneficial  in  practice,  both  in  the 
education  of  the  consumer  and  in  establishing  better  re- 
lations. 

3.  The  duties  of  the  meter  readers  are  not  confined  to 
simply  taking  off  the  position  of  the  dial  hands.  It 
is  the  commonly  accepted  idea  that  cheap  labor  should  be 
employed  on  this  work,  and  its  duty  confined  to  the  mere 
taking  of  the  reading.  If  this  practice  be  followed,  it  be- 
comes necessary  to  employ  inspectors  to  examine  and 


GENERAL  POLICY.  157 

clean  the  meters  at  regular  intervals  if  an  efficient  meter 
service  is  the  end  sought.  The  cost  of  meter  readers  and 
inspectors  to  the  central  station  is  greater  than  if  the  offices 
of  the  two  are  combined  by  making  the  meter  reader 
an  inspector  as  well. 

4.  The  practice  of  giving  the  meter  a  thorough  cleaning 
once  every  two  months  cannot  be  too  highly  commended, 
and  if  the  meter  has  commutator  and  brushes,  the  passing 
of  a  piece  of  linen  tape  between  them  and  pulling  briskly 
back  and  forth  gives  a  high  polish  which  reduces  friction. 
At  the  same  time  that  the  meter  is  cleaned  the  jewel  is 
examined  and,  if  defective,  renewed  as  well  as  the  removable 
shaft  end. 

5.  The  life  of  a  jewel  varies  with  the  treatment  it 
receives.     Vibration  and  dust  tend  to  shorten  this  life,  and 
if  the  vibration  be  excessive  it  becomes  extremely  short. 
However,  outside  of  the  effects  of  vibration  and  dust,  the 
life  of  a  jewel  has  a  somewhat  definite  period,  after  which  it 
rapidly  deteriorates.     In  order  to  avoid  the  evil  effects  of 
letting  defective  jewels  remain  in  the  meter,  introducing  a 
friction  which  causes  a  direct  loss  of  revenue,  it  is  evident 
that  some  definite  system  of  jewel  renewals  must  be  in- 
stituted.    If  a  meter  contain  a  defective  jewel  there  is  no 
economy  in  letting  it  remain  in  the  meter,  and  the  con- 
dition of  meter  service  in  which  no  defective  jewels  are 
allowed  to  remain  in  would  certainly  be  far  superior  to  any 
other.     Therefore,  when  the  meter  reader  cleans  the  meter 
at  periods  of  two  months  apart,  if  he  renews  the  jewel  at 
the  same  time,  he  eliminates  the  loss  due  to  defective 
jewels.     He  need  not  test  the  jewel  to  see  if  it  needs  re- 
newing, after  the  system  is  instituted  the  old  jewel  is  taken 
out  and  the  new  one  put  in,  the  old  jewel  being  tested  after 
it  is  brought  back  to  the  meter  department.     The  good 


15.8  AMERICAN  METER  PRACTICE. 

jewels  are  sent  out  again ;  the  defective  ones  discarded.  In 
this  way  nothing  is  wasted,  and  the  bad  jewels  are  effectively 
weeded  out  of  the  system.  The  meter  reader's  duties  then 
are  to  read  every  meter  on  his  route,  to  inspect,  clean  and 
renew  jewels  in  every  other  meter.  The  greater  part  of  the 
time  taken  in  reading  is  consumed  in  getting  from  meter  to 
meter,  the  actual  time  of  taking  the  reading  is  small;  hence, 
the  cutting  down  of  the  route  owing  to  the  extra  time  con- 
sumed in  cleaning  every  other  meter  is  not  as  great  as 
appears  at  first  sight.  If  a  reader  on  a  given  route  can 
read  100  meters  per  day,  on  the  same  route  he  can  read  75 
meters  and  clean  every  other  one,  the  reduced  distance  by 
leaving  off  2  5  meters  more  than  compensates  for  time  taken 
in  cleaning  37  meters. 

As  a  concrete  example,  suppose  a  central  station  em- 
ploys four  meter  readers  and  three  inspectors,  the  inspector 
cleaning  and  renewing  jewels  once  every  two  months,  the 
addition  of  two  more  inspectors  would  take  the  place  of  four 
meter  readers  and  a  much  more  efficient  service  secured. 
In  other  words  you  eliminate  the  going  over  of  the  same 
ground  by  different  men  for  different  purposes,  and  secure 
better  service  at  less  expense  by  combining  their  offices. 
While  cleaning  the  meter  a  rough  test  can  be  made  of  its 
correctness  on  light  loads;  in  this  way  many  defective 
meters  are  replaced  to  advantage  by  new  ones. 

The  examination  of  the  meter  loop  to  see  that  the  cus- 
tomer's installation  is  all  recorded,  and  the  lookout  at  all 
times  for  ways  and  means  of  beating  the  meters,  are  among 
the  many  if  lesser  duties  of  the  readers.  A  good  meter  reader 
must  be  alert,  intelligent,  courteous.  It  pays  to  employ 
good  men  for  any  service,  it  pays  particularly  well  here. 


CHAPTER  XIII. 
Reading    Meters. 

Meter  reading  is  a  simple  operation,  yet  many  fail  to  grasp 
the  relations  of  the  hands  of  the  dials  to  one  another,  in 
such  a  way  as  to  avoid  making  mistakes  in  taking  a  reading. 

The  majority  of  meters  have  five  circles  composing  the 
dial  face,  and  each  circle  is  divided  into  ten  divisions. 
Under  or  above  each  circle  is  marked  the  amount  of 
energy  each  one  indicates  in  a  complete  revolution.  These 
units  are  usually  expressed  in  watt  hours,  and  the  lower 
right  hand  circle  is  usually  marked  "1,000  watt  hrs.," 
indicating  that  one  revolution  of  this  circle  registers  1,000 
watt  hours,  and  each  division  in  it  100  watt  hours.  The 
next  circle,  reading  from  right  to  left,  will  be  marked  10,000 
watt  hours,  and  so  on  in  multiples  of  ten  to  the  last  circle 
at  the  left  hand  side  of  the  dial  face.  Therefore,  reading 
from  right  to  left,  each  circle  indicates  ten  times  the 
amount  of  its  predecessor,  hence,  each  division  on  a  circle 
indicates  an  entire  revolution  of  the  preceding  one.  If 
this  relation  be  borne  in  mind  it  is  almost  impossible  to 
make  a  mistake  in  reading  the  meter,  even  if  the  hands  be 
slightly  misplaced.  The  hands  on  the  first,  third  and 
fifth  circles  turn  clockwise,  and  on  the  other  two  counter- 
clockwise, which  leads  to  confusion  with  a  beginner  when 
first  attempting  to  read  a  meter. 

The  reading  is  started  with  the  dial  indicating  1,000 
watt  hours  and  the  indication  of  the  hand  put  down  at  the 
nearest  100  watt  hours.  The  second  circle  is  likewise 
marked  down,  the  number  being  placed  to  the  left  of  the 

159 


160 


AMERICAN  METER  PRACTICE. 


first  circle's  indication.  The  third,  fourth  and  fifth  dials 
are  likewise  recorded. 

The  relation  of  the  dials  to  each  other  must  be  borne  in 
mind  when  reading,  and  it  must  be  remembered  that,  when 
a  hand  stands  between  two  numbers,  the  one  last  passed  is 
the  one  to  record. 

The  subject  can  be  better  explained  by  means  of  ex- 
amples, a  few  of  which  are  herewith  given. 

In  Fig.  69,  we  have  900  watt  hours  registered  as  the  first 
circle  and  the  hand  of  the  second  dial  apparently  on  o.  It 
is  evident  that  this  cannot  be  on  zero,  as  the  space  from  9 


10,000,000 


1,000,000 


I00,0u0 


10,000 


1,000 


FIGS.  69  (TOP  ROW  OF  DIALS), 70  (MIDDLE  ROW)  AND  71  (BOTTOM  ROW). 

to  o  represents  one  whole  revolution,  circle  i ;  hence,  we 
read  this  9,900.  In  dial  3,  the  hand  is  again  on  zero,  but 
it  cannot  be  actually  zero  as  the  previous  dial  did  not 
complete  a  whole  revolution,  therefore  we  read  it  9,  and 
the  reading  stands  99,900.  Circle  4,  is  read  9  in  the  same 
manner  and  the  total  reading  is  999,900.  On  the  fifth 
circle  the  pointer  is  on  i,  but,  as  dial  4  did  not  complete  its 
revolution,  we  read  this  zero.  It  is  very  easy  for  any 
one  not  bearing  in  mind  the  relation  of  the  different  circles 


READING  METERS.  161 

to  each  other  to  make  this  dial  read  1,000,900  watt 
hours. 

In  Fig.  70,  we  have  a  very  easy  reading — 253,400  watt 
hours,  and  in  Fig.  71,  a  succession  of  5*5,  making  a  reading 
5,555,500  watt  hours.  Asi,ooowatt  hours  is  one  kilowatt 
hour,  the  total  indications  of  the  dial  face  with  multiplier 
i  is  10,000  kilowatt  hours. 

After  one  becomes  familiar  by  practice  with  reading 
meters,  the  dials  may  be  read  from  left  to  right  with  facility, 
but  the  safer  way  is  from  right  to  left.  Nearly  all  meters 
have  multipliers  in  the  larger  sizes  by  which  the  indication 
on  the  dial  face  is  multiplied  to  obtain  the  number  of 
watt  hours  that  has  been  used.  In  some  of  the  small  sizes, 
the  indication  of  the  dial  face  is  multiplied  by  a  fraction  to 
obtain  the  true  watt  hours. 

Some  manufacturers,  instead  of  using  a  multiplier  for 
different  sized  meters,  change  the  relation  of  the  worm  gear 
reduction  between  the  dial  train  and  the  revolving  arma- 
ture shaft  in  order  to  make  the  dial  face  always  read 
directly  in  watt  hours.  This  practice  is  to  be  commended, 
as  it  tends  to  simplify  the  records  and  eliminate  errors  by 
getting  the  wrong  multipliers  recorded  through  oversight. 

Ampere  hour  meters  have  dial  faces  which  indicate 
ampere  hours  instead  of  watt  hours.  The  readings  are 
taken  in  the  same  manner  as  described  for  watt  hour  meters. 

The  majority  of  consumers  of  electric  current,  particu- 
larly store  keepers,  mill  owners  and  factories,  would  like 
to  know  how  to  read  their  meters  and  figure  out  the  bills 
from  the  readings.  A  knowledge  by  them  of  their  daily 
consumption  of  current  would  enable  them  in  many  in- 
stances to  institute  economies  which  would  result  in  a 
material  reduction  in  their  lighting  or  power  bill. 

We  will  suppose,  foi  example,  that  the  reading  of  the 


162  AMERICAN  METER  PRACTICE. 

meter  on  May  ist  was  986,600  watt  hours,  and  on  May  zoth 
it  was  1,230,600  watt  hours,  the  consumption  of  current 
for  the  ten  days  would  be  250,000  watt  hours,  or  250 
kilowatt  hours.  To  obtain  the  bill,  the  kilowatt  hours  are 
multiplied  by  the  amount  charged  per  kilowatt  hour 
which  we  will  suppose  to  be  10  cents.  Twenty-five  dollars 
($25.00)  would  be  the  required  bill.  If  the  dial  face  carried 
a  multiplier,  the  consumption  would  have  been  multiplied  by 
it  and  then  by  the  price  per  kilowatt  hour.  Whether  for  light 
or  power  the  bill  would  be  determined  in  the  same  manner. 

As  a  1 6  c.  p.  lamp,  when  burned  for  one  hour,  registers 
50  watt  hours  on  the  dial  face,  a  rough  estimate  can  be 
readily  made  by  the  consumer  to  ascertain  the  correctness 
of  his  meter.  If  ten  16  c.  p.  lamps  are  turned  on  for  one 
hour,  the  meter  will  register  it  correctly,  500  watt  hours. 
A  percentage  fast  or  slow  would  be  readily  noticeable  in  a 
reading  of  this  size,  and  the  consumer  in  this  way  can 
satisfy  himself  as  to  the  correctness  of  his  meter.  If  this 
were  more  universally  done,  much  idle  complaint  by  the 
consumer  would  be  avoided. 

To  facilitate  the  duties  of  the  meter  reader,  a  meter  slip 
carrying  blank  dial  faces  is  used,  and  the  indications  of  the 
hands  are  marked  down  as  they  appear.  This  serves  as  a 
check  on  the  reading  recorded,  and  enables  a  "checker," 
when  the  slips  are  turned  into  the  office,  to  verify  the  cor- 
rectness of  the  reading.  After  a  dial  face  has  been  in  use 
for  some  time,  the  fifth  circle  at  the  left  hand  may  complete 
a  total  revolution  between  readings.  In  that  event, 
the  previous  reading  is  subtracted  from  10,000,000,  and 
the  reading  found  on  the  dial  when  read  will  be  added  to  the 
amount  thus  obtained.  In  other  words,  the  dial  will  have 
started  all  over  again.  This  frequently  happens,  and 
sometimes  leads  to  confusion  in  the  mind  of  the  consumer. 


CHAPTER  XIV. 
Value  of  Losses  in  Meters  Relative  to  Income. 

The  meter  has  been  one  of  the  most  potent  agencies  in 
the  development  of  the  central  station  for  the  distribution 
of  electrical  energy  for  light  and  power  purposes,  but  the 
history  of  this  development  is  interesting  from  many 
standpoints. 

Steam  engines  and  water  wheels  have  been  brought  to 
ever-increasing  heights  of  efficiency,  due  in  great  measure 
to  the  exacting  conditions  imposed  in  the  various  classes  of 
central  station  duty.  In  the  past  few  years,  the  gas 
engine  and  steam  turbine  have  been  perfected  to  such  a 
degree  that  they  bid  fair  to  dispute  in  some  measure  the 
claim  for  first  places  as  prime  movers  with  the  steam 
engine. 

On  the  purely  electrical  side,  the  rapid  growth  of  the 
dynamo  and  motor  both  in  size  and  efficiency,  and  the 
many  uses  to  which  the  latter  is  put,  have  divided  the  field 
into  many  provinces,  distinct,  yet  united  by  their  common 
ancestry. 

The  no  less  rapid  perfection  of  the  arc  and  incandescent 
lamp  has  ever  widened  the  lighting  field,  until  to-day 
electricity  holds  first  place  as  the  illuminant  of  the  world. 
In  the  early  days  of  electric  lighting,  when  the  commercial 
side  of  the  problem  was  first  attacked,  it  was  recognized 
that  the  broad  principle  upon  which  the  commerce  of  the 
world  is  carried  on  constituted  the  only  equitable  and 
profitable  basis  on  which  lighting  could  be  done;  namely, 
the  paying  for  exact  value  received.  In  commercial  life 

163 


164  AMERICAN  METER  PRACTICE. 

we  meter  every  product  that  is  sold  either  by  weight, 
measure  or  some  known  standard.  It  is  unnecessary,  how- 
ever, in  ordinary  transactions  to  do  this  automatically,  or 
to  still  further  complicate  matters  by  bringing  in  the 
element  of  time.  The  commercial  measurement  of  elec- 
tricity, as  we  have  seen,  must  combine  all  of  these  factors, 
and  many  hundreds  of  patents  testify  to  the  work  which 
has  been  done  along  these  lines.  The  idea  of  charging  so 
much  per  month  for  16  c.  p.  lamp  installed  was  a  crude 
one,  but  examples  of  it  are  still  found  in  many  commun- 
ities. The  lamp  then  becomes  a  crude  meter,  and  at  the 
first  glance  it  is  seen  that  this  is  merely  an  approximate 
way  of  securing  an  income  and  gives  rates  to  different 
consumers  which  vary  over  wide  ranges. 

The  failure  of  many  plants  to  earn  dividends  was  directly 
traceable  to  this  method  of  selling  current,  and,  except 
where  the  load  and  hours  are  fixed  quantities,  it  is  universal 
modern  practice  to  meter  all  installations  whether  for  light 
or  power.  But  the  mere  fact  of  placing  a  meter  on  a  cir- 
cuit does  not  insure  immunity  from  loss  to  the  central 
station;  the  meter  needs  care  and  proper  attention,  other- 
wise its  readings  are  not  a  true  record  of  the  current  con- 
sumed in  the  circuit. 

In  the  general  consideration  of  the  various  engineering 
problems  of  central  station  management,  the  meter  is 
usually  relegated  to  somewhere  near  the  tenth  place  in 
matter  of  importance.  Its  use  is  well  recognized,  but  the 
necessities  of  its  maintenance  and  operation  are  usually 
neglected,  until  to-day  it  is  the  least  understood  of  all 
branches  of  electrical  engineering,  even  by  those  who  are 
acknowledged  authorities. 

It  is  easy  to  build  a  meter  having  a  commercial  efficiency 
of  from  98  to  99  per  cent,  on  half  and  full  loads,  and,  at  first 


l(    UNIVERSITY 
LOSSES  RELATIVE    TO 


glance,  this  appears  to  be  a  very  creditable  performance, 
but  the  question  is — what  will  this  same  meter  do  commer- 
cially on  from  2  to  10  per  cent,  of  its  load? 

The  average  load  on  the  meters  of  a  central  station  lies, 
as  a  rule,  under  10  per  cent,  of  their  capacity;  this  fact 
emphasizes  the  extreme  importance  of  having  the  meters 
register  correctly  on  this  load. 

In  taking  up  the  discussion  of  the  losses  in  the  meters  and 
their  relations  to  income,  it  is  necessary  to  outline  in  a 
general  way  the  main  factors  of  cost  of  generation  and 
sale  of  current  from  a  central  station. 

The  three  main  factors  necessary  to  secure  the  suc- 
cessful operation  of  a  central  station  are:  ist,  Never 
failing  integrity  of  service ;  2d,  A  market  for  the 
current  ;  3d,  Proper  registration  of  current  sold.  The 
first  and  second  of  these  factors  will  be  assumed  to  exist. 
They  lie  outside  the  scope  of  this  discussion,  and  may 
be  considered  as  the  prime  requisites  of  any  commer- 
cial undertaking.  On  the  purely  operative  side  of 
the  business,  the  management  of  the  meter  department 
easily  stands  first  in  its  effect  on  the  economy  of  the  sell- 
ing of  current  from  central  stations.  The  details  of  this 
management  are  set  forth  in  Chapter  XII.  The  cost  of 
current  to  the  central  station  is  determined  by  its  operat- 
ing expenses  and  fixed  charges  per  unit  of  current  generated. 
The  fixed  charge,  after  the  investment  is  made,  remains  a 
fairly  constant  factor  per  unit  of  current  generated,  hence 
economy  in  operating  expenses  becomes  the  chief  end  of 
the  central  station  manager.  It  is  necessary,  for  the  sake 
of  brevity,  that  we  accept  the  conditions  which  we  find 
prevalent  in  the  actual  cost  of  generation  of  current  with- 
out going  into  details.  In  this  connection  a  brief  summary 
of  what  is  considered  fairly  representative  cost  in  the  art, 


166  AMERICAN  METER  PRACTICE. 

as  it  is  to-day,  will  be  given.  The  cost  of  generating  a  kilo- 
watt hour  varies  with  the  locality,  cost  of  fuel,  etc.,  but  the 
range  may  be  taken  from  one-half  to  one  and  a  half  cents 
per  kilowatt  hour  at  the  switchboard.  It  is  assumed  that 
the  plant  is  of  modern  construction,  with  compound  or  triple 
expansion  engines  as  prime  movers,  and  having  the  usual 
auxiliaries  pertaining  to  the  best  modern  practice.  Under 
such  conditions  one-half  cent  per  kilowatt  hour  would 
represent  extremely  favorable  conditions  and  one  and 
one-half  cent  per  kilowatt  hour  good  conditions,  so  that  an 
average  of  one  cent  per  kilowatt  hour  may  be  taken  as  a 
basis  of  cost  for  the  purpose  of  showing  the  relative  cost  of 
generation  to  income  in  contrast  with  the  meter  loss  to 
income.  In  assuming  one  cent  per  kilowatt  hour  as  cost 
at  the  switchboard  it  is  necessary  to  assign  values  to  the 
various  items  which  go  to  make  up  this  total,  so  as  to  show 
what  percentage  the  different  items  of  cost  bear  to  income. 

Fuel  will  be  taken  as  three  pounds  per  kilowatt  hour  at 
$2.00  per  ton,  making  the  cost  for  fuel  per  kilowatt  hour 
.0033  cents,  leaving  .0067  to  represent  labor,  maintenance, 
oil,  etc. 

Let  us  assume  an  average  daily  output  of  30,000  kilo- 
watt hours,  and  the  usual  line  and  meter  loss  of  25  per  cent, 
between  the  bus  bar  and  the  total  amount  registered  at 
consumer's.  Let  us  assume,  also,  an  average  net  price  of 
ten  cents  per  kilowatt  hour  as  registered  by  the  consumer's 
meters.  Then  the  net  price  at  the  switchboard  is  7^  cents 
per  kilowatt  hour.  From  the  above,  the  ratio  between  the 
cost  of  coal  and  the  net  amount  received  per  kilowatt  hour 
is  roughly  i  to  22,  or  the  cost  of  coal  is  only  4^  per  cent,  of 
the  net  income. 

Any  loss  or  saving  in  the  coal  pile  of  from  10  to  20  per  cent, 
only  effects  the  net  income  by  a  fraction  of  one  per  cent. 


LOSSES  RELATIVE   TO  INCOME.  167 

Under  the  conditions  assumed,  the  total  cost  of  genera- 
tion is  13  H  per  cent,  of  the  net  income,  and,  even  if  the 
most  rigid  economies  permissible  to  good  practice  were 
instituted,  and  the  cost  per  kilowatt  hour  reduced  thereby 
to  .75  cents,  a  saving  of  only  3^  per  cent,  of  the  net  in- 
come would  be  the  result. 

It  is  the  writer's  intention,  not  to  belittle  any  practice 
which  reduces  the  cost  of  generation,  but  merely  to  point 
a  comparison  between  those  losses  and  a  loss  which  is  in 
excess  of  their  total;  namely,  the  loss  in  the  meters  them- 
selves. 

It  may  be  safely  stated  that  in  a  carefully  operated 
central  station  the  net  saving  in  generation,  which  could 
be  effected  by  the  most  rigid  economies,  will  not 
exceed  3  to  4  per  cent,  of  the  net  income.  Any 
saving  in  the  cost  of  generation  is  limited  in  extent; 
that  is,  can  never  approach  closely  to  its  limit  in 
the  present  illustration  of  13  1-3  per  cent,  of  the  net 
income. 

In  taking  the  total  loss  in  lines  and  meters  at  25  per 
cent.,  the  average  condition  of  the  large  central  station  in 
America  is  represented.  The  usual  loss  attributable  to 
meters  is  15  per  cent.,  and  10  per  cent. is  the  usual  line  loss. 
The  loss  in  transmission  from  the  switchboard  to  the  con- 
sumer will  be  made  as  large  or  small  as  we  please,  according 
to  the  amount  of  copper  used  in  distributing  the  current. 
The  10  per  cent,  loss  in  the  lines  means  that  the  generating 
equipment  must  be  1 1  per  cent,  larger  than  that  necessary 
to  meet  the  demands  at  the  consumer's  connection. 

Any  reduction  in  line  loss  means  larger  copper  invest- 
ment, any  increase  in  line  loss  means  larger  generating 
capacity,  so  that  there  is  established  somewhere  an  eco- 
nomical balance  which  varies  for  different  conditions,  but 


168  ,      AMERICAN  METER  PRACTICE. 

may  be  roughly  taken  as  corresponding  to  a  10  per  cent, 
loss  in  the  distributing  system. 

This  line  loss  of  10  per  cent,  in  the  example  given  above 
means  that  only  27,000  kilowatt  hours  are  delivered  to 
the  consumer,  of  which  only  22,500  kilowatt  hours 
are  registered  after  the  15  per  cent,  meter  loss  is 
deducted. 

The  line  loss  should  be  included  in  the  cost  of  generation, 
since,  if  the  line  loss  be  reduced,  a  reduced  amount  of  current 
is  generated  at  a  reduced  cost,  and  vice  versa. 

The  meter  loss,  on  the  contrary,  is  in  current  actually 
delivered  and  used  by  the  consumer,  but  not  paid  for  by 
him. 

The  loss  is  of  such  a  nature  as  to  affect  the  dividend 
directly  by  its  amount.  The  general  expenses  of  the 
plant  and  system  are  not  altered  whether  it  is  prevented 
or  not.  It  seems  incredible  that  a  loss  of  this  magni- 
tude, the  prevention  of  which  would  effect  a  saving  that 
would  offset  the  entire  cost  of  generation,  should  be 
tolerated. 

The  peculiar  conditions  prevalent  in  central  station 
practice  bring  about  a  condition  of  affairs  which  is  very 
trying  to  the  correct  registration  of  current.  The 
meter  capacity  installed  usually  equals  the  load  con- 
nected to  the  lines.  The  maximum  output  of  a 
central  station  feeding  a  distributing  system  for  light 
and  power  rarely  exceeds  20  per  cent,  of  the  load 
connected.  The  minimum  output  falls  as  low  as  2  to  3 
per  cent,  of  the  load  connected,  or  the  meter  capacity. 
Thus  it  is  evident  that  the  meters,  as  a  whole,  register 
on  from  2  to  20  per  cent,  of  their  rated  capacity,  the 
mean  load  falling  as  low  as  6  to  10  per  cent,  of  their 
capacity. 


LOSSES  RELATIVE   TO   INCOME.  169 

When  the  problem  is  looked  at  broadly  in  this  light  it  is 
not  difficult  to  see  why  a  meter  having  a  high  commercial 
efficiency  on  half  and  full  loads  fails  to  register  properly 
on  a  mean  load  of  from  6  to  10  per  cent,  of  its 
capacity. 

As  an  example  of  the  trying  conditions  under  which 
meters  work,  let  us  take  a  store  having  100— i6's  installed. 
During  the  day,  from  7  A.  M.  until  4  P.  M.,  assume  that 
2-1 6 's  are  burned,  and  that  from  4  P.  M.  to  6  P.  M.  an 
average  of  50  lights  is  used.  After  6  P.  M.,  until  7  A.  M. 
next  morning,  one  light  is  left  burning.  If  the  current  were 
correctly  registered,  the  amounts  for  the  different  hours 
would  be  as  follows: 

7  A.  M.  to  4  P.  M 9  hours  at  $0.02     $0.18 

4  P.  M.  "    6  2  .50        i .  oo 

6       "        "    7  A.  M 13       "       "       .01          .03 

$1.31 

In  commercial  practice  a  meter  of  100  light  capacity 
does  not  register  one  or  two  lights  with  any  degree  of 
accuracy,  in  all  probability  not  running  at  all  on  one  light. 
The  loss,  in  this  instance,  per  day  on  the  small  burning 
of  31  cents  would  be,  say,  25  cents  or  18  per  cent,  of  the 
amount  registered.  This  case  in  hand  represents  a  preva- 
lent condition.  There  are  exceptions  where  the  meter  is 
always  run  at  a  load  in  which  it  is  practically  correct. 
Again,  the  conditions  may  be  easily  more  adverse.  At  any 
rate,  they  are  sufficiently  adverse  to  cause  a  general  loss 
of  15  per  cent,  of  the  current  delivered,  and  that  too  by 
meters  which,  on  loads  of  20  per  cent,  of  their  capacity,  are 
commercially  correct. 

The  solution  of  this  problem  would  be  one  of  the  greatest 


170  AMERICAN  METER  PRACTICE 

benefits  to  central  stations.  That  solution  so  far  has 
not  been  reached  by  any  meter  on  the  market,  but 
manufacturers  are  constantly  bringing  out  improved 
types  of  meters  with  higher  light  load  efficiencies 
and  a  general  improvement  may  be  looked  for  in  a  few 
years  when  the  older  types  of  meters  wear  out  and  are 
discarded. 


CHAPTER  XV. 
Differential  Rating. 

Electric  current  is  charged  for  at  so  much  per  unit,  with 
discounts  of  varying  amounts  applying  to  the  different 
number  of  units  used  in  a  specified  time.  A  careful  study 
of  the  load  line  of  a  central  station  reveals  the  fact  that 
between  certain  hours  of  the  day  a  great  deal  more  current 
is  used  than  at  any  other  time.  A  plant  must  be 
installed  which  will  be  capable  of  meeting  the  larger 
demand,  and  this  means  that  it  will  lie  idle  for  a  great 
part  of  each  day. 

The  investment  in  this  required  generating  capacity, 
which  is  only  used  for  a  short  period,  increases  the  cost  of 
furnishing  current  during  the  hours  of  "peak"  over  that  of 
the  normal  load.  However,  by  charging  a  uniform  rate 
per  unit  for  each  24  hours,  an  average  rate  may  be  struck 
which  will  yield  a  profit  on  the  business  done. 

The  plan  of  differential  rating  has  secured  quite  a  strong 
foothold,  and  the  theory  of  it  has  been  worked  out  along 
two  distinct  lines, — one  to  make  the  maximum  demand 
of  the  consumer  at  any  time  during  the  month  a  basis 
of  rating  his  charge  per  unit,  and  the  other  to  charge  at 
a  higher  rate  per  unit  for  current  used  in  the  hours  of 
"peak." 

The  Wright  demand  meter  is  the  best  known  device  for 
the  first  method  of  differential  rating.  The  principle  of 
the  recording  thermometer  is  used,  and  the  instrument  con- 
.sists  of  a  U-shaped  glass  tube  with  a  bulb  at  each  end, 
partly  filled  with  sulphuric  acid,  and  hermetically  sealed. 

171 


172  AMERICAN  METER  PRACTICE. 

On  the  upper  bulb  a  strip  of  platinoid  is  wound,  this  plat- 
inoid strip  is  placed  in  series  with  the  current  flowing,  and 
is  heated  thereby.  The  heat  generated  in  the  strip  ex- 
pands the  air  in  the  bulb,  and  forces  the  liquid  up  the  other 
leg  of  the  U  into  the  remaining  bulb,  where  it  overflows 
into  a  recording  tube  which  is  graduated  to  represent 
amperes  flowing.  The  instrument  can  be  reset  by  allow- 
ing the  liquid  to  flow  from  the  indicating  tube  by  tilting  the 
instrument.  The  origin  of  the  system  was  in  Brighton, 
England. 

The  demand  meter  is  placed  in  series  with  a  recording 
wattmeter,  and  the  total  number  of  watt  hours  registered 
is  checked  against  the  maximum  demand  to  determine 
the  number  of  hours  per  day  that  the  maximum  demand 
was  used.  Whatever  the  comparison  in  the  case,  the 
length  of  time  per  day  that  the  consumer  could  have  used 
his  maximum  demand  is  noted  and  the  charge  adjusted. 
The  number  of  hours  of  high  charging  are  usually  varied  in 
summer  and  winter,  say  a  half  hour  per  day  in  summer  and 
one  to  two  hours  in  winter.  The  remainder  of  the  amount 
registered  is  charged  for  at  a  reduced  rate.  The  indicator 
will  not  record  short  circuits  or  demands  of  only  a  few 
minutes,  but  takes  fully  ten  minutes  to  indicate  its  load. 

The  idea  is  to  make  each  consumer  pay  for  his  propor- 
tion of  plant  investment  necessary  to  meet  the  peak  of  the 
load  he  uses.  In  other  words,  if  the  consumer  use  the 
same  amount  of  current  each  hour  of  the  24,  a  minimum 
plant  investment  with  a  maximum  return  would  be 
the  result.  If  the  total  energy  generated  in  24  hours 
were  used  in  12  hours,  double  the  generating  and  line  capac- 
ity would  have  to  be  installed  to  get  the  same  revenue. 
If  the  consumer  use  current  for  one  hour  per  day  to  the 
same  amount  that  his  neighbor  does  in  24  hours,  the  plant 


DIFFERENTIAL   RATING.  173 

investment  for  one  would  be  24  times  as  great  as  for  the 
other,  and  the  same  revenue  would  be  derived  from  both. 

But  the  weak  spot  in  the  Wright  demand  system  is 
that  the  consumer  does  not  lend  himself  readily  to  the 
solving  of  central  station  problems,  and  prefers  to  buy 
electricity  at  a  fixed  price  per  unit.  Again,  it  is  no  induce- 
ment for  a  consumer  to  burn  light  when  he  does  not  need 
it,  no  matter  how  cheap  it  is. 

A  modification  of  the  Wright  demand  system  was  put 
on  the  market  by  Edward  Halsey,  of  Chicago.  The  ad- 
vantages of  his  device  lie  in  doing  away  with  an  addi- 
tional resistance  in  circuit  with  the  line  and  in  its 
adaptability  to  either  two  or  three-wire  meters.  In  a 
recording  meter  having  a  magnetic  drag,  the  armature 
shaft  is  cut  in  two  parts  and  connected  by  a  sleeve  and 
ratchet  coupling.  The  upper  portion  of  the  shaft  carrying 
the  armature  carries  a  pointer  which  travels  over  a  gradu- 
ated scale  laid  off  on  the  meter  disk.  The  upper  and  lower 
portions  of  the  shaft  are  coupled  by  a  graduated  spring 
which  allows  the  pointer  to  assume  a  position  equal 
to  the  torque  on  the  armature.  When  this  torque  is  re- 
moved, the  ratchet  prevents  the  pointer  from  traveling 
back  to  zero,  thus  leaving  a  permanent  indication  of  the 
maximum  demand.  A  viscous  fluid  is  placed  in  the  sleeve 
which  retards  the  movement  of  the  shaft  in  such  a  manner 
as  to  prevent  the  pointer  from  recording  momentary  over- 
loads or  short  circuits. 

The  principles  of  rating  in  this  and  the  Wright  systems 
are  the  same,  the  difference  lying  only  in  the  means  used  for 
obtaining  the  maximum  demand. 

Another  system,  which  does  away  with  any  device  at  all, 
is  based  upon  the  assumption  that  the  maximum  demand 
will  be  the  consumer's  installation  or  some  known 


174  AMERICAN  METER  PRACTICE. 

percentage  of  it.  This  system  is  limited  in  its  application 
and  is  not  at  all  suitable  for  stores  or  warehouses  where  a 
large  number  of  lamps  are  installed,  but  is  applicable 
where  only  a  small  number  are  used.  The  rating  is  the 
same  as  in  the  Wright  system. 

The  two-rate  meter  placed  on  the  market  by  the  General 
Electric  Co.,  affords  another  system  of  differential  rat- 
ing with  a  different  theory  at  its  base.  The  meter  carries 
two  dial  trains  and  a  self-winding  clock  for  switching  over 
clutch  mechanism  at  suitable  hours  for  throwing  the  dif- 
ferent dials  on  or  off.  For  instance,  if  "the  peak"  lie  be- 
tween the  hours  of  5  and  7  P.  M.,  one  dial  is  used  to  meter 
all  the  energy  consumed  during  these  hours  and  the  other 
dial  that  consumed  in  the  other-  22.  Such  a  system  can 
be  carried  out  successfully  from  a  mechanical  standpoint, 
but  the  effect  of  the  practice  has  been  to  drive  the  con- 
sumer to  using  some  cheap  illuminant  during  the  hours 
of  high  charging. 

It  is  true  that  long  hour  burning  is  encouraged  by  the 
cheaper  rate  given  during  the  day  and  latter  part  of  the 
night.  The  consumer's  peak  may  not  correspond  with  the 
station  peak,  and  if  such  be  the  case,  the  principles  of  the 
demand  system  are  violated,  as  the  consumer  fails  to  pay 
in  proportion  to  his  plant  investment. 

It  is  not  believed  that  differential  rating  is  a  permanent 
solution  of  the  problem  of  charging  for  current.  If  every 
consumer  were  an  electrical  engineer  and  were  willing  to  abide 
by  his  faith  in  differential  rating,  the  scheme  would  be 
extremely  practical  and  just ;  but  as  such  is  not  the  case,  and 
as  every  other  commercial  problem  in  the  law  of  demand 
and  supply  has  its  peaks  which  are  worked  out  on  a 
fixed  rate  of  charge  instead  of  differential  rate,  he 
demands  the  same  with  regard  to  his  use  of  electric  current. 


DIFFERENTIAL  RATING.  175 

If  a  differential  rate  scheme  be  adopted,  it  is  necessary, 
in  order  to  avoid  the  errors  of  the  system  already  named, 
to  secure  a  complete  load  curve  of  the  consumer's  burning 
each  day. 

A  device  that  would  take  the  total  number  of  watt 
hours  registered  for  a  given  period  and  break  it  up  into  its 
component  parts,  telling  how  long  the  maximum  load 
was  on,  how  long  the  minimum,  and  also  when  no  lights 
were  burned  at  all  each  day,  would  give  a  complete  load 
curve  of  the  consumer's  burning  and  furnish  a  perfect 
basis  for  differential  charging.  A  chart  ammeter  in 
series  with  the  meter  would  answer  the  purpose,  or  pref- 
erably still,  an  integrating  movement  attached  to  the  dial 
train.  The  integrating  movement  attached  to  the  dial 
train  would  be  worked  in  conjunction  with  a  clock  and  a 
pointer,  actuated  by  a  cam  on  one  of  the  dial  spindles, 
made  to  dot  off  any  given  watt  hour  unit  consumed  in  a 
certain  time. 

Any  auxiliary  device  increases  the  meter  investment 
and  also  the  clerical  work,  and  all  of  these  things  must  be 
taken  into  account  in  the  consideration  of  differential 
rating.  The  problems  to  be  solved  for  any  central  station 
are  these: 

The  average  cost  of  generating  a  kilowatt  hour. 

The  saving  that  would  be  effected  by  the  installing  of 
storage  batteries  and  the  leveling  of  the  "peaks"  in  the 
load  curve  as  against  the  maintenance  of  these  peaks  and 
differential  rating. 

The  installing  of  storage  batteries  has  the  two  advantages 
of  leveling  the  load  line  and  making  the  cost  per  kilowatt 
for  each  hour  of  the  day  the  same. 

If  differential  rating  be  used  to  secure  the  proper  in- 
come, the  cost  of  generating  a  kilowatt  hour  remains  the 


176  AMERICAN  METER  PRACTICE. 

same  and  we  have  a  very  unsatisfactory  method  of  obtain- 
ing an  income.  While  the  general  scheme  of  differential 
charging  is  to  discourage  the  peak  burning,  nevertheless 
it  remains  and  always  will  remain  as  long  as  the  contrasts 
of  night  and  day  exist. 

From  a  careful  consideration  of  all  the  conditions,  it 
appears  conclusively  that  the  ultimate  solution  of  the 
basis  of  charge  must  follow  in  the  lines  of  general  com- 
mercial practice;  a  fixed  rate  per  unit. 

In  large  communities,  such  as  our  cities  of  New  York, 
Boston,  Chicago,  Philadelphia,  the  whole  trend  of  the  age 
is  towards  consolidation.  The  railroad  and  electric 
interests  are  frequently  affiliated  if  they  do  not  actually 
belong  to  the  same  people.  The  current  for  an  entire  city 
may  be  furnished  from  one  plant  or  group  of  plants  so 
arranged  that  each  individual  plant  is  worked  to  its  highest 
efficiency. 

The  ever-growing  uses  to  which  electricity  is  put  are 
evening  up  the  load  curves,  and  the  individual  ceases  to 
become  a  short  hour  burner.  The  man  in  his  home  uses 
electricity ;  when  he  rides  down  town  to  the  office  he  uses 
electricity;  at  the  office,  lights  and  fans  contribute  to  his 
comfort;  when  he  goes  to  dinner  he  rides  on  the  car  again. 
After  dinner  he  dresses  by  electric  lights  to  go  out  to  the 
theatre  or  club,  or  if  he  stays  at  home  he  still  uses  elec- 
tricity. If  he  keep  an  automobile,  it  is  charged  from 
12  at  night  to  7  A.  M.,  so  we  find  the  individual 
practically  a  24-hour  consumer  of  electric  current.  This 
current  is  all  furnished  by  a  number  of  individuals,  A.  B. 
&  C.,  associated  together  in  a  company.  It  is  a  matter  of 
engineering  ability  to  determine  whether  it  pays  in  any 
given  set  of  conditions  to  even  up  the  load  line  in  a  plant  by 
means  of  storage  batteries,  and  this  question  is  for  A.  B.  & 


DIFFERENTIAL   RATING.  177 

C.,  to  decide.  The  individual  claims  he  is  a  long  hour  con- 
sumer and  entitled  as  such  to  the  best  rates,  and  there- 
fore is  not  called  upon  to  help  finance  the  investments  of 
A.  B.  &  C.,  other  than  to  purchase  current  at  a  fixed  price. 
In  the  general  plan  of  electrical  development  it  does  not 
pay  to  discourage  the  consumer  from  using  current  at  any 
hour  of  the  day,  but  rather  he  should  be  encouraged  to  use  all 
he  can  at  any  hour.  If  told  that  between  the  hours  of  5  and  7 
in  the  evening  A.  B.  &  C.  find  that,  owing  to  poor  engineer- 
ing, they  are  unable  to  furnish  him  with  as  much  current 
as  they  would  like  and  will  have  to  charge  a  higher  price 
at  these  hours,  in  order  to  discourage  its  use,  the  con- 
sumer naturally  rebels.  The  consumer  has  worries  of  his 
own,  he  does  not  care  to  be  eternally  bothered  about  his 
use  of  electricity,  but  wants  to  purchase  current  at  a  fixed 
price  per  unit  as  he  does  every  other  commodity  he  uses. 

Differential  rating  is  a  temporary  makeshift  which  is 
bound  to  go  before  the  demands  of  the  consumer  for  a 
fixed  price  per  unit.  This  has  been  recognized  by  a  num- 
ber of  the  best  managed  plants  in  this  country,  and  all 
schemes  for  differential  rating  are  avoided  as  being  im- 
practical and  cumbersome. 

We  cite,  as  an  instance,  the  policy  of  New  York  Edison 
Company,  which  has  for  a  number  of  years  steadily  de- 
creased the  price  per  unit  with  increased  demand,  and  has 
successfully  carried  on  a  large  and  lucrative  business  on 
the  basis  of  fixed  charges  per  unit. 

American  practice  has  been  slow  to  take  hold  of  the 
differential  rate  idea,  although  a  number  of  large  plants 
are  using  "Wright"  meters  on  their  systems  with  more 
or  less  success.  From  the  trend  of  the  times  it  may 
safely  be  predicted  that  within  ten  years'  time  the  differ- 
ential rate  will  be  a  thing  of  the  past, 


CHAPTER  XVI. 
Elements   of   Photometry. 

The  1 6  candle-power  lamp  was,  as  it  is  yet,  to  a  great 
extent  a  meter.  The  flat  rate  system  uses  the  16  candle 
lamp  as  a  basis  of  charge  on  a  supposed  number  of  hours 
burning.  It  is  recognized  that  this  is  a  very  crude  way  of 
metering  current,  as  the  factor  of  time,  one  of  the  most 
important  elements,  is  unrecorded.  The  metering  or 
measuring  the  candle  power  of* lamps  is  a  determination 
of  their  efficiency  as  regards  consumption  of  current  per 
candle,  as  well  as  the  mere  determination  of  their  candle 
power.  Hence  the  measuring  of  candle  power  is  closely 
allied  to  measurement  of  current  and  is  properly  included 
in  the  same  discussion. 

The  measurement  of  light  offers  many  difficulties  not 
encountered  in  the  measurement  of  such  things  as  time 
and  weight.  The  candle  is  the  unit  to  which  light  intens- 
ities are  referred.  The  origin  of  this  unit  was  quite 
natural,  as  the  candle  was  one  of  the  earliest  and  most  uni- 
form of  light-giving  sources. 

But  this  unit,  while  approximately  constant,  is  subject 
to  considerable  variation,  according  to  the  size  of  wick, 
quality  of  the  fuel  and  height  of  the  flame,  besides  the 
influences  of  atmospheric  conditions.  The  standard  Eng- 
lish candle  is  supposed  to  give  unit  light  with  a  flame  1.8 
inch  high,  and  a  consumption  of  120  grains  of  material — 
spermaceti  and  wick— per  hour.  The  difficulties  of  obtain- 
ing a  correct  reading  from  such  a  standard  are  great  and 
have  led  to  the  seeking  of  various  standards,  all  of  which 

178 


ELEMENTS   OF   PHOTOMETRY.  179 

are  more  or  less  open  to  objection.  Some  of  the  best  known 
of  these  may  be  briefly  mentioned  without  going  into  a 
detailed  description. 

The  pentane  lamp  has  many  excellent  qualities.  Pentane 
is  a  refined  distillate  of  gasolene,  and  in  its  pure  state  is  an 
excellent  fuel  for  a  standard  light-giving  source.  The 
difficulty  of  obtaining  it  in  a  pure  state  is  so  great  that  it 
has  been  practically  abandoned  as  a  standard.  The 
pentane  is  fed  by  a  wick  to  the  flame,  which  burns  inside 
a  metallic  chimney  having  a  slit  and  a  gauge  for  indicating 
the  height  of  the  flame. 

The  Methven  screen  arrangement,  one  of  the  well-known 
secondary  standards,  consists  of  an  argand  gas  flame  burn- 
ing inside  the  usual  glass  chimney.  On  the  outside  of  the 
chimney  there  is  placed  a  metallic  screen  with  a  slit  which 
allows  a  light  intensity  of  two  candles  to  pass.  The  flame 
burns  at  a  height  of  three  inches.  The  varying  quality  of 
the  gas  is  the  greatest  objection  to  this  light  as  a  primary 
standard,  although  it  may  answer  very  successfully  as  a 
secondary  standard. 

The  Hefner- Alteneck  lamp,  burning  pure  amyl-acetate, 
fulfills  more  fully  the  requirements  of  a  reliable  standard 
than  any  other  known  standard,  and  has  been  adopted 
provisionally  by  the  American  Institute  of  Electrical 
Engineers  as  the  best  candle-power  standard  yet 
obtained.  For  a  more  detailed  description  of  this  and  the 
other  standards,  the  writer  takes  pleasure  in  referring  the 
reader  to  a  series  of  articles  by  Prof.  Wilbur  M.  Stine,  in  the 
March,  April  and  May  (1899)  issues  of  the  American 
Electrician. 

Our  appreciation  of  the  intensity  of  light  is  at  present 
confined  to  one  organ,  the  human  eye,  and  as  every  eye 
has  its  own  particular  "personal  equation,"  the  comparison 


180  AMERICAN  METER  PRACTICE. 

of  light  intensities  with  any  standard  must  vary  by  an 
appreciable  per  cent,  according  to  the  observer.  Hence, 
when  we  speak  of  the  "candle-power"  of  any  source  of 
light,  it  is  more  or  less  a  comparative  term. 

There  are,  then,  two  sources  of  error  to  contend  with  in 
the  measurement  of  light,  a  variable  standard  and  the 
personal  error  of  the  observer.  In  spite  of  these  difficulties 
the  commercial  measurement  of  various  light  sources  has 
reached  a  stage  where  the  error  amounts  to  an  insignifi- 
cant percentage. 

A  few  years  ago  we  rarely  heard  of  the  photometer 
outside  of  a  laboratory.  The  advent  of  the  incandescent 
lamp  has  been  the  cause  of  the  familiarization  of  this 
instrument.  There  was  little  need  commercially  to 
measure  the  candle-power  of  a  gas  or  oil  flame;  the  light- 
giving  qualities  of  the  one  are  fixed  by  the  size  of  the 
orifice  of  the  burner,  quality  and  pressure  of  the  gas ;  those 
of  the  other,  principally  by  its  size  and  the  condition  of 
the  wick.  The  deterioration  of  the  candle-power  of  a  gas 
flame  is  dependent  primarily  on  the  source  of  supply, 
while  that  of  the  incandescent  lamp,  assuming  the  voltage 
constant,  depends  upon  its  age.  This  decrease  in  illuminat- 
ing power,  due  to  aging,  it  has  been  the  chief  desire  of  man- 
ufacturers to  overcome.  Their  degree  of  success  will  be 
brought  out  more  fully  later.  It  is  apparent  that  if  the 
modern  incandescent  lamp  remained  of  a  constant  light- 
giving  quality,  the  factory  test  would  be  all  that  would  be 
needed  to  establish  its  candle-power  until  it  was  burnt  out, 
and  that  the  deterioration  of  the  candle-power  with  age  is 
the  chief  cause  of  the  development  of  the  commercial 
photometer. 

An  incandescent  lamp  of  low  efficiency  can  be  made, 
however,  which,  when  properly  aged,  will  remain 


ELEMENTS   OF  PHOTOMETRY.  181 

practically  constant  in  candle-power  if  burned  at  the  prop- 
er voltage.  Such  lamps  are  tested  by  a  primary  standard 
in  a  very  careful  manner,  and  can  then  be  used  as  secondary 
standards  with  a  fair  degree  of  accuracy ;  hence  the  use  of 
oil  and  gas  flames  as  secondary  standards  has  given  place 
to  a  properly  aged  and  tested  incandescent  lamp.  This 
practice  has  many  advantages  besides  ease  of  manipulation 
in  testing,  the  chief  of  which  are  slow  deterioration  of  the 


FIG.  72. 


standard  and  the  same  character  of  light  as  the  lamp  to  be 
tested. 

The  commercial  photometer  with  an  incandescent 
standard  is  very  simple  and  lends  itself  readily  to  the 
unskilled  handling  which  it  frequently  encounters.  Two 
excellent  types  of  photometers  designed  for  the  com- 
mercial testing  of  lamps  are  the  Queen  Standard  photom- 
eter and  the  Deshler-McAllister  instrument,  both  well 


182  AMERICAN  METER  PRACTICE. 

suited  to  the  needs  of  the  central  station.  Both  of  these 
photometers  were  designed  to  supply  the  need  for  a  rapid 
and  fairly  accurate  instrument.  In  photometers  of  this 
class  the  time  element  of  a  lamp  test  is  the  most  important 
mechanical  factor  connected  with  the  instrument,  affecting 
directly  also  its  value  as  a  commercial  success. 

The  Queen  Standard  photometer,  which  is  represented 
by  Fig.  72,  consists  of  two  cast-iron  pedestals  carrying  a 
rack  on  which  are  mounted  the  photometer  carriage  and 
scale.  The  carriage  is  rolled  to  any  desired  position  and 


b 


FIG.  73. 

the  reading  taken  directly  from  the  scale.  Two  styles  of 
screens  are  used,  the  Lummer-Brodhun  and  Bunsen.  The 
former  is  about  three  or  four  times  more  sensitive  than  the 
Bunsen,  but  the  latter  may  be  read  more  quickly.  Either 
may  be  used,  but  when  the  number  of  lamps  to  be  tested  is 
very  large,  the  Bunsen,  owing  to  its  quick  manipulation, 
has  much  to  recommend  it. 

The  Lummer-Brodhun  screen  consists  usually  of  an 
opaque  piece  of  gypsum  and  a  set  of  right -angle  prisms 
with  their  hypothenusal  faces  partially  coinciding,  and 


ELEMENTS   OF  PHOTOMETRY. 


183 


mirrors  so  arranged  as  to  reflect  the  light  from  both  sides  of 
the  screen,  as  indicated  in  Fig.  73,  where  5  is  the  screen, 
M,  M,  the  mirrors,  and  P,  /?,  the  prisms.  One  prism,  p, 
transmits  the  light  and  the  other,  P,  reflects  it,  giving 
a  double  field  of  light  which  is  viewed  through  the  telescope 
at  E.  The  two  beams  of  light  are  lettered  a  and  b.  If 
they  be  of  unequal  power,  the  two  "fields"  of  light  present 
a  marked  contrast,  and  only  become  the  same  when  both 
sides  of  the  screen  are  equally  illuminated.  The  field  is  a 


round  spot  and  that  of  b  is  a  ring  surrounding  this  spot. 
The  contrast  is  so  marked  that  a  balance  can  be  obtained 
with  great  nicety.  % 

The  Bunsen  screen,  represented  diagrammatically  by 
Fig.  74  is  probably  more  familiar,  consisting  simply  of  a 
piece  of  opaque  paper,  S,  with  a  grease  spot  on  it.  Two 
mirrors,  M,  M,  are  set  at  such  an  angle  as  to  reflect  this 
spot  and  allow  the  observer  to  judge  of  the  relative  intens- 
ities of  the  fields  on  opposite  sides  of  it.  When  the  spot 
appears  of  equal  strength  in  both  mirrors  the  screen  is 


184  AMERICAN  METER  PRACTICE. 

receiving  the  same  illumination  on  each  side,  and  the 
candle-power  is  read  directly  from  the  scale. 

The  left-hand  pedestal  carries  the  standard  lamp,  in 
series  with  which  is  a  regulating  rheostat  to  enable  it  to 
burn  at  the  exact  voltage  at  which  it  gives  16  c.-p.  The 
right-hand  pedestal  carries  the  lamp  to  be  tested,  mounted 
in  a  revolving  socket.  A  special  arrangement  allows  the 
lamp  to  be  put  in  or  removed  without  stopping  the  socket. 
A  controller  permits  the  socket  to  be  run  at  the  desired 
speed  of  180  revolutions  per  minute.  An  adjustable 
rheostat  is  also  in  series  with  the  lamp  to  be  tested,  allow- 
ing the  voltage  across  the  lamp  to  be  made  anything  de- 
sired within  a  small  range.  Between  the  pedestals  is 
placed  a  table  upon  which  rest  two  voltmeters  and  an 
ammeter.  One  voltmeter  is  connected  across  the  termi- 
nals of  the  standard  lamp  and  the  other  across  the  terminals 
of  the  lamp  to  be  tested;  the  ammeter  is  placed  in  series 
with  the  tested  lamp.  One  voltmeter  may  be  dispensed 
with  by  putting  in  a  throw-over  switch,  connecting  the  two 
lamps  to  one  voltmeter  and  taking  readings  on  each 
alternately. 

The  Deshler-McAllister  photometer,  manufactured  by 
the  Electric  Motor  and  Equipment  Company,  is  made  in 
the  portable  form,  but,  when  equipped  with  a  rotating 
socket  and  mounted  on  a  table  or  bench,  it  becomes  suitable 
for  station  work.  (See  Fig.  75.)  The  instrument  is  about 
five  feet  long  and  can  be  folded  up.  The  working  standard 
of  light  is  a  duplex  oil  lamp  at  the  right-hand  end  of  the 
instrument.  This  lamp  is  lighted  and  allowed  to  burn  20 
minutes;  then  it  is  calibrated  by  a  standard  incandescent 
lamp.  Calibration  is  effected  by  placing  a  standard  lamp 
in  the  socket  which  the  tested  lamp  occupies,  placing  the 
screen  at  the  16  c.-p.  mark  on  the  scale,  and  adjusting 


ELEMENTS   OF   PHOTOMETRY. 


185 


the  oil  flame  until  a  balance  of  "fields"  is  effected, 
screen  is  of  the  Bunsen  type,  riding  over  a  celluloid 
on  which  the  candle-power  is 
marked.  The  station  type  of 
instrument  is  now  fitted  with  a 
rotating  lamp-socket  at  the  left- 
hand  end  and  an  ordinary  lamp- 
socket  at  the  right,  the  oil  lamp 
being  dispensed  with. 

Each  lamp  has  in  series  with 
it  a  regulating  rheostat  for 
adjusting  the  voltage.  The 
standard  incandescent  lamp  has 
many  advantages  over  the  oil 
flame,  and  its  adoption  has 
greatly  improved  the  instru- 
ment. Two  black  cloth  screens 
shield  the  observer's  eye  from 
the  rays  of  the  standard  and 
tested  lamps.  A  voltmeter 
and  an  ammeter  are  either 
placed  on  the  bench  or 
mounted  on  the  back  of  the 
instrument  in  plain  view. 
For  rapid  work  the  large  illum- 
inated dial  type  of  instrument 
mounted  directly  behind  the 
carriage  has  many  advantages, 
being  in  plain  view  and  easily 
read  by  the  observer  simply 
raising  his  eyes. 

Assuming  that  a  commercial 
photometer,  such  as  one  of 


The 
scale 


186 


AMERICAN  METER  PRACTICE. 


those  described,  has  been  selected,  in  which  the  standard 
is  an  incandescent  lamp,  the  arrangement  of  the  circuits 
for  testing  may  be  made  in  several  ways,  three  of  which 
are  given,  ist,  A  separate  circuit  for  each  lamp.  26., 
The  same  circuit  for  both  lamps,  with  equalizer.  3d,  A 
three-wire  circuit  fed  by  a  small  storage  battery.  These 
three  methods  all  assume  that  the  secondary  standard  is  a 
properly  aged  and  tested  incandescent  lamp  obtained 
.from  some  reliable  laboratory. 

The  first  method,  in  which  a  separate  circuit  is  em- 


FIG.  76. 


ployed  for  each  lamp,  is  roughly  illustrated  by  Fig.  76, 
where  A  is  the  lamp  to  be  tested  in  the  rotating  socket, 
and  B  is  the  standard  lamp.  Both  lamps  are  fed  from  a 
common  two-wire  service,  C,  D.  This  is  preferable  to  feed- 
ing the  lamp  from  a  three-wire  service,  as  the  fluctuation 
in  voltage  on  either  side  of  such  a  circuit  may  not  be  of 
the  same  period  or  amount  and  thus  cause  an  unevenness 
in  the  intensity  of  either  light,  which  is  avoided  by  using  a 
two-wire  service.  Variable  resistances,  E  and  F,  are 
connected  in  series  with  each  lamp  respectively,  and  so 


ELEMENTS   OF  PHOTOMETRY. 


constructed  that  a  small  movement  of  the  sliding  con- 
tact produces  only  a  slight  variation  in  resistance.  A 
common  form  of  such  resistance  is  a  cylinder  of  insulating 
material  wrapped  spirally  with  bare  resistance  wire  over 
which  slides  a  contact  ring. 

In  series  with  the  lamp,  A,  is  placed  an  ammeter,  Am, 
and  a  voltmeter,  Vm,  is  so  arranged  that  by  means  of  a 
double-throw  switch  it  can  be  connected  to  the  terminals 
of  either  lamp.  The  voltmeter  and  ammeter  are  not 
essential  if  a  mere  comparison  of  light  intensity  be  made,  as 
any  fluctuation  in  the  service  e.m.f.  affects  both  lamps 
alike,  but  if  a  wattage  test  be  conducted  at  the  same  time, 
the  two  instruments  are  indispensable.  The  ammeter 
reading  multiplied  by  the  voltmeter  reading  gives  the  watt 
reading,  but  if  the  voltage  be  fairly  steady,  a  close  approxi- 
mation of  the  wattage  may  be  had  by  simply  observing 
the  ammeter  and  getting  the  watt  values  from  a  pre- 
viously prepared  table. 

If  the  service  be  taken  from  the  street  mains  and  the 
lamps  to  be  tested  be  for  service  on  these  mains,  the 
standard  at  B  should  be  of  a  lower  voltage  and  the  vari- 
able resistance  should  be  adjusted  to  give  this  lamp  the 
voltage  at  which  it  should  burn.  If  a  wattage  test  be  made 
on  the  lamps,  it  is  extremely  annoying  to  have  the  volt- 
age remain  below  the  normal  for  any  length  of  time,  and 
for  this  reason  it  is  best  to  have  the  service  come  directly 
from  the  bur  bars  in  the  station,  and  adjust  the  voltage 
at  lamps  to  the  proper  value  by  means  of  the  variable 
resistances.  The  voltage  at  the  bus  bars  should  be  kept 
very  steady,  and  the  resistances  in  series  with  the  lamps 
after  being  once  adjusted  should  need  little  attention.  If 
a  wattage  test  be  made  on  each  lamp,  the  voltmeter  and 
ammeter  are  left  in  circuit  with  the  lamp  being  tested. 


188 


AMERICAN  METER  PRACTICE. 


In  this  connection  of  lamps  a  removal  of  the  lamp,  A, 
only  causes  a  rise  in  potential  at  B,  equal  to  the  drop  on 
the  wires,  C,  D,  caused  by  the  current  consumed  by  A, 
hence,  the  voltage  of  the  standard,  B,  is  practically  un- 
affected by  the  removal  of  A.  In  testing  a  number  of 
lamps,  however,  it  is  found  that  they  will  vary  considerably 
in  current  consumed,  and  this  fact,  owing  to  the  variable 
drop  caused  thereby  in  the  resistance,  E,  makes  the  lamp 
at  A  burn  at  a  different  relative  voltage  to  B,  unless  the 
resistance,  E,  is  constantly  varied  to  suit  each  lamp  tested. 
Therefore,  when  a  comparison  is  made  an  error  is  intro- 
duced, unless  the  resistance,  E,  is  changed  to  give  the  same 
relative  voltage  across  A  that  B  receives.  To  do  this,  two 


JFio.  77. 


voltmeter  readings  have  to  be  taken,  and,  in  the  meantime, 
the  voltage  on  C,  D  may  have  varied,  vitiating  the  results. 
A  way  of  overcoming  this  trouble  is  shown  in  Fig.  77, 
where  the  same  methods  of  connection  are  used,  but  an 
equalizing  wire  connected  between  E  and  F  places  the 
resistances  in  parallel  when  the  two  lamps  are  in  circuit. 
This  connection  is  to  be  broken  when  A  is  removed  from  its 
socket.  For  convenience,  the  breaking  of  the  equalizer 
connection  is  so  arranged  in  practice  as  to  be  accomplished 


ELEMENTS   OF   PHOTOMETRY. 


189 


by  the  same  operation  that  removes  the  lamp,  A,  from  its 
socket.  The  voltmeter  is  connected  to  the  equalizer  wire 
and  the  wire,  C,  and  indicates  the  common  voltage  on  both 
lamps.  The  wattage  of  the  lamp,  A,  is  the  product  of  the 
ammeter  reading  and  the  voltmeter  reading  when  the 
equalizer  is  closed.  In  both  of  these  first  two  methods, 
the  candle-power  over  small  ranges  of  voltage  has  been 
assumed  to  vary  on  each  lamp  in  the  same  proportion. 
But  this  assumes  the  same  constant  for  each  lamp,  which 
may  or  may  not  exist. 

The  standard  lamp  and  the  lamp  to  be  tested  may  not  be 
possessed  of  the  same  physical  characteristics  or  the  same 


Equalizing  Wire 

FIG.  78. 


ratios  of  graphitic  carbon  to  base  carbon  in  their  filaments, 
any  difference  in  either  of  which  would  have  a  direct  in- 
fluence on  their  light-giving  qualities  at  different  voltages. 
To  eliminate  all  errors  of  this  character,  the  third  method 
wherein  a  storage  battery  is  employed  particularly  com- 
mends itself  to  favor. 

In  Fig.  78,6*  and  D  represent  two  terminals  of  a  storage 
battery  of  a  sufficient  number  of  cells  to  give  double  the 
potential  needed  for  the  lamps,  at  1.8  volts  per  cell.  From 
these  cells  is  led  off  a  three-wire  service  with  two  neutral 
conductors,  /  and  J,  connected  respectively  to  one  end  of 


190  AMERICAN  METER  PRACTICE. 

the  variable  resistances,  E  and  F,  in  series  with  the  lamps ,. 
A  and  B.  Leads,  L  and  AT,  complete  the  circuit  through 
the  lamps  to  the  positive  and  negative  ends  of  the  battery. 
This  battery  may  vary  in  ampere  capacity,  but  for  an 
ordinary  central  station  a  capacity  of  10  ampere  hours  at 
the  discharge  rate  of  i  J  amperes  per  hour  is  sufficiently  large. 

The  use  of  the  battery  provides  for  each  lamp  an  isolated 
circuit  of  its  own  of  absolutely  constant  potential.  The 
standard  lamp  at  B  is  adjusted  to  its  proper  voltage  and 
remains  without  need  of  further  attention.  The  object 
of  splitting  the  neutral  is  to  remove  the  slight  fluctuation 
caused  by  the  drop  in  this  conductor  when  the  lamp  at  A 
is  removed.  One  side  of  the  battery  alone  could  be  used 
for  both  lamps,  but  the  variable  demand  upon  it  would 
cause  a  slight  fluctuation  of  the  voltage  at  the  standard 
lamp,  which  should  be  entirely  eliminated  for  quick 
work.  The  voltmeter  is  connected  through  a  double- 
pole  switch  across  the  terminals  of  either  of  the  lamps,  A 
and  B,  as  in  first  method,  and  is  left  in  circuit  across  A 
when  a  test  is  being  made.  Occasionally  a  reading  across 
B  is  taken,  to  see  if  the  voltage  has  varied  by  the  dis- 
charging of  the  battery. 

The  lamp,  A,  is  in  a  circuit  which  receives  a  constant 
potential,  but  the  potential  across  the  lamp  varies  with  the 
current  taken  by  the  lamp,  hence,  the  variable  resistance, 
E,  is  so  placed  as  to  be  readily  under  the  control  of  the 
operator. 

The  arrangement  of  the  dark  room  is  a  matter  which 
should  be  carefully  planned  to  enable  quick  and  accurate 
work  to  be  done.  The  reading  of  the  instruments  should 
take  as  little  time  as  possible,  and,  for  this  reason,  the  large 
illuminated  dial  type  of  meter  placed  directly  back  of  the 
photometer  screen  is  the  best  for  quick  work.  These  meters 


ELEMENTS   OF  PHOTOMETRY.  191 

may  be  mounted  in  any  convenient  manner,  the  controlling 
switches  being  within  easy  reach  of  the  operator. 

The  scale  divisions  of  the  voltmeter  should  be  large, 
which  condition  may  be  secured  by  using  an  instrument 
the  range  of  which  extends  only  about  15  volts  above  and 
below  the  voltage  of  the  lamps  to  be  tested.  The  ammeter 
need  not  read  higher  than  two  amperes  in  o.oi  =  ampere 
divisions.  The  scales  of  the  instruments  should  be  elevated 
slightly  above  the  level  of  the  top  of  the  photometer  screen ; 
the  values  can  then  be  read  at  a  glance. 

Unless  a  specific  test  is  being  made,  an  adjustable  pointer 
on  the  ammeter  is  of  great  assistance  in  rejecting  all  lamps 
above  a  certain  wattage,  as  it  can  be  set  at  a  given  value 
and  every  lamp  which  runs  the  needle  over  this  point 
rejected  at  once. 

The  variable  resistance  on  the  lamp  to  be  tested  should 
be  within  easy  reach  of  the  left  hand;  in  fact,  the  opera- 
tor's left  need  never  leave  it,  as  his  right  can  be  used  to 
shift  the  screen. 

In  operating,  the  lamps  to  be  tested  in  the  rotating 
socket  are  removed  by  a  boy  who  disposes  of  them  accord- 
ing to  the  reader's  call  "good"  or  "bad."  Usually  the 
speed  of  the  testing  is  entirely  dependent  upon  the  quick- 
ness with  which  the  boy  at  the  sockets  can  handle  the 
lamps. 

The  reader's  eyes  should  be  shielded  from  the  rays  of 
the  standard  and  tested  lamps,  and,  as  it  takes  several 
minutes  for  the  eyes  to  adjust  themselves  to  reading  the 
screen,  the  reader  should  not  expose  his  eyes  to  extraneous 
light  between  readings.  In  testing  a  large  number  of 
lamps  where  extreme  accuracy  is  not  desired,  advantage 
must  be  taken  of  every  factor  which  reduces  the  duration 
of  a  test. 


192  AMERICAN  METER  PRACTICE. 

THE  IMPORTANCE  OF  PHOTOMETRY  TO  CENTRAL  STATIONS. 

The  success  which  the  electric  light  has  attained  is 
based  primarily  on  its  intrinsic  merits,  its  convenience, 
cleanliness  and  adaptability,  rendering  it  superior  to  any 
other  commercial  light,  but  not  necessarily  cheaper.  Its 
march  forward  to  the  final  limit  of  universal  use  depends 
then  on  two  main  underlying  qualities ;  first,  its  superiority 
over  other  lights;  and  second,  its  ability  to  compete 
commercially  with  other  light-giving  sources.  Almost 
every  day  brings  forth  some  new  form  of  light,  which  the 
enthusiastic  inventor  claims  will  render  the  electric  light 
obsolete  in  a  very  short  time.  The  best  answer  to  such 
claims  is  found  in  the  rapid  enlargement  of  the  electric 
central  stations  in  every  part  of  the  world. 

The  price  of  electricity  has  shown  within  the  past  few 
years  a  tendency  to  become  less,  as  more  economical 
methods  of  generation  are  utilized,  but  it  is  safe  to  say  that 
no  very  radical  departure  in  present  prices  will  come  about 
as  long  as  the  efficiency  of  the  incandescent  lamp  remains 
at  its  present  low  figure.  The  lamp  may  be  considered  the 
keystone  of  the  entire  structure ;  it  is  the  final  link  in  the 
series  of  transformations  of  energy  which  take  place  be- 
tween the  coal-pile  and  the  light,  and  on  its  economy  (other 
conditions  being  favorable)  depends  the  earning  power  of 
the  central  station. 

The  economy  of  the  incandescent  lamp  must  be  viewed 
from  two  standpoints,  that  of  the  consumer  and  that  of  the 
central  station.  The  light  emitted  from  an  incandescent 
lamp  filament  increases  rapidly  as  the  voltage  across  the 
lamp  rises,  and  if  the  voltage  be  maintained  above  normal 
for  any  length  of  time,  the  life  of  the  lamp  is  very  much 
shortened.  The  higher  the  voltage  is  raised,  the  greater 


ELEMENTS   OF  PHOTOMETRY.  193 

becomes  the  efficiency  of  the  lamp;  that  is,  the  more  light 
per  watt  of  energy  it  gives. 

Viewed  from  the  consumer's  standpoint,  the  lamp 
should  not  last  more  than  a  few  hours  for  him  to  get  the 
best  returns  for  his  money.  This  would  necessitate  such 
frequent  renewals  by  the  central  station  that  the  cost 
of  furnishing  lamps  would  be  prohibitive.  Viewed  from 
the  central  station's  standpoint,  the  lamp  which  lasts  the 
greatest  number  of  hours  is  the  best  lamp;  that  is,  it  needs 
fewest  renewals,  and  hence  is  the  most  economical. 

Between  the  two  extremes  here  presented  there  must 
be  a  mean  which  should  combine  the  good  qualities 
of  both  conditions  in  the  greatest  possible  degree. 
The  perfect  lamp  would  maintain  a  constant  candle- 
power  for  an  indefinite  period  with  small  expenditure  of  en- 
ergy ;  the  modern  commercial  lamp  endeavors  to  give  a  fairly 
uniform  candle-power  for  a  limited  period  with  an  expendi- 
ture of  energy  varying  from  three  to  four  watts  per  candle. 

It  has  been  found  that  the  long-life  lamp  is  usually  of 
low  efficiency  to  start  with,  and  this  efficiency  becomes 
lower  as  the  number  of  hours  the  lamp  burns  increases, 
until  in  many  instances  the  efficiency  becomes  as  low  as 
10  watts  per  candle.  The  amount  of  energy  consumed 
per  candle  renders  the  lamp  in  this  condition  uncom- 
mercial and  destroys  the  quality  of  its  light.  In  other 
words,  the  consumer  agrees  to  pay  for  light  at  the  rate  of 
three  to  four  watts  per  candle  and  will  not  consent  to  pay  at 
the  rate  of  10  watts  per  candle  for  an  inferior  light.  The 
central  station,  then,  in  order  to  fulfil  its  contract  with  the 
consumer,  must  see  to  it  that  the  amount  of  light  furnished 
per  watt  is  maintained  at  somewhere  near  the  required  figure. 

Assuming  the  average  total  life  of  the  lamp  to  be  2,000 
hours,  the  power  to  be  16  candle-power  at  3.1  watts  per 


194  AMERICAN  METER  PRACTICE. 

candle  at  the  start,  and  8  candle-power  at  6  watts  per 
candle  at  the  end  of  the  2,000  hours,  the  mean  candle-power 
and  efficiency  over  the  total  period  may  be  roughly  taken 
as  12  candle-power  at  4.5  watts  per  candle;  in  other  words, 
this  might  be  the  candle-power  and  efficiency  at  the  end  of 
1,000  hours.  A  new  lamp  of  this  quality  (12  candle- 
power  at  4.5  watts  per  candle-power)  would  be  considered 
uncommercial  on  a  circuit  having  close  voltage  regulation. 
Why,  then,  should  it  be  tolerated  simply  because  it  has 
had  the  misfortune  to  burn  i  ,000  hours  ? 

The  lamp  reaches  an  uncommercial  state  at  some  point 
previous  to  this  time,  and  the  results  of  a  great  number 
of  tests  have  shown  that  the  commercial  period  of  a  high- 
efficiency  lamp  is  reached  in  about  600  hours  burning. 
The  average  3.1  watt-lamp  burning  at  an  initial  candle- 
power  of  16  has,  at  the  expiration  of  600  hours,  a  candle- 
power  of  13,  and  an  efficiency  of  3.7  watts  per  candle, 
which  may  be  considered  the  end  of  the  commercial  life  of 
the  lamp.  The  average  efficiency  of  the  whole  period  is 
14.5  candles  at  3.38  watts  per  candle. 

For  a  central  station  to  compete  successfully  with 
Welsbach  and  other  lights,  the  candle-power  of  the 
lamps  of  the  entire  service  must  be  maintained  at  a  high 
standard.  To  do  this  successfully  a  system  of  periodic 
renewals  must  be  instituted,  the  frequency  of  which  can  be 
roughly  estimated  from  the  consumer's  bills.  If  a  consumer 
having  10  lamps  develop  a  gross  bill  of  $10  a  month  at  one 
cent  per  lamp  hour,  the  average  service  per  lamp  is  i  oo  hours, 
and  the  renewals  of  lamps  need  only  be  made  twice  a  year. 

The  maintenance  of  a  clean  lighting  service,  without  any 
waste  in  the  lamps  displaced  by  renewals,  necessitates  the 
photometering  of  all  the  lamps  returned.  The  lamps  in 
the  consumer's  premises  frequently  become  fly-specked 


ELEMENTS   OF   PHOTOMETRY.  195 

and  covered  with  dust  so  that  it  is  impossible  to  judge  of 
the  true  candle-power  of  a  lamp  until  it  is  cleaned.  As 
the  lamps  must  be  changed  by  cheap  labor,  it  is  best  not  to 
invest  this  labor  with  powers  of  discrimination,  but 
to  have  all  the  lamps  in  a  given  installation  changed 
regardless  of  their  appearance. 

Some  idea  of  the  total  cost  of  renewals  in  lamps  may  be 
gained  for  any  station  by  proceeding  as  follows:  In  a 
typical  plant,  assume  1000  16  c.-p.  lamps  connected,  and 
a  gross  income  of  $3,650  per  annum  at  £  cent  per  lamp 
hour.  Then  the  average  income  per  day  will  be  $10, 
corresponding  to  1333  lamp  hours  a  day,  or  1.3  hours  per 
lamp  per  day.  Allowing  600  hours  per  lamp  as  the  com- 
mercial life,  each  lamp  would  last  461  days,  requiring  the 
renewal  of  about  800  lamps  per  year.  This  figure  is  some- 
what higher  than  would  be  met  in  practice,  but  it  amounts 
to  less  than  five  per  cent,  of  the  gross  income.  The  in- 
creased income  from  good  service  would  more  than  counter- 
balance the  cost.  This  policy  on  the  part  of  a  central 
station  would  be  very  popular  and  could  be  used  effect- 
ively in  soliciting  new  business  and  settling  disputed  bills, 
not  to  mention  the  inducement  it  gives  the  consumer  to 
burn  more  light. 

To  return  to  the  photometric  features  of  the  work,  the 
renewal  of  lamps  should  be  carried  out  daily,  and  the 
returned  lamps  cleaned  preparatory  to  testing.  The 
tested  lamps  are  divided  into  two  classes,  those  testing 
between  13  and  16  candle-power  are  retained  as  a  sort  of 
second-class  stock,  and  those  testing  up  to  16  candle- 
power  and  over  are  treated  specially,  and  considered  as 
first-class  stock. 

If  the  first-class  stock  be  in  the  majority,  the  lamps  are 
tested  for  this  class  first;  if  the  second-class  stock  be  the 


196  AMERICAN  METER  PRACTICE. 

largest,  the  lamps  are  tested  by  setting  the  photometer 
screen  at  13  candle-power  and  rejecting  all  under  this 
candle-power.  The  good  lamps  left  are  then  tested  by 
setting  the  screen  at  16  candle-power  and  sifting  out  the 
separate  classes.  By  following  this  order  the  lamps  are 
subjected  to  the  smallest  amount  of  handling. 

The  second-class  stock  is  preferably  used  for  special 
illuminations  and  outdoor  work,  but  if  there  be  not  enough 
demand  in  this  line  to  balance  the  supply  of  such  stock,  it 
may  be  judiciously  issued  to  points  near  the  plant  where 
a  higher  voltage  is  maintained.  This  second-class  stock 
has  a  short  average  life.  The  lamps  testing  16  candle- 
power  have  their  stubs  buffed  and  the  glass  thoroughly 
cleaned,  any  defaced  labels  are  removed  and  new  ones  put 
on,  and  the  lamp  is  made  to  look  as  good  as  new  in  every 
respect.  Such  stock  is  issued  on  equality  with  new  lamps. 
The  cost  of  photometering  is  very  small ;  the  entire  cost  of 
cleaning,  photometering  and  buffing  the  stubs  is  about 
J  cent  per  lamp. 

In  carrying  out  the  system  of  renewals  the  area  cov- 
ered should  be  divided  into  districts,  and  these  districts 
carefully  gone  over  at  regular  intervals,  the  work  being 
so  arranged  that  a  specified  number  of  lamps  are  changed 
each  day.  Boys  are  usually  employed  in  this  class  of  work ; 
no  special  intelligence  is  required,  as  the  work  consists  in 
simply  removing  the  lamp  and  putting  in  a  new  one. 

The  system  of  free  renewals  is  no  new  experiment.  Its 
utility  has  been  well  established,  and,  when  practiced  in 
conjunction  with  a  photometer,  as  outlined  in  the  fore- 
going paragraphs,  it  furnishes  an  ideal  method  of  main- 
taining the  commercial  efficiency  of  the  entire  lighting 
system  at  its  proper  value  without  incurring  the  slightest 
loss  due  to  waste  by  such  renewals. 


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=r— — — 


OCT  17  1935 
MAR  10 


v 


YC   19596 


1*( 


r> 


